I wish to know how I made an "a priori" assumption that the Catholic Church is the true church. First of all I stated that the scriptures indicate quite obviously that there is a visible church that was set in motion by Christ himself so that Christians may be guided into truth rather than through ones own interpretations.(Matthew 16, 1 Timothy 3, John 17) This is not an a priori assumption in regards to the validity of Catholicism as it does not state anything as to who the true church is(granted I would believe it is the Catholic Church). However simply by going over this step there are a few other viable options the Eastern Orthodox Church, Oriental Orthodox Church, and Churches of the East for example. My statement would simply cross off Protestantism as Protestantism rejects the idea of a "visible entity" in the sense we are speaking of. Granted the protestant can and should question as to how I come up with such a conclusion and how it is not merely my own personal conclusion or why it is any more valid than the protestant who claims the church is fully invisible this leads me to my next point lets look at some quotes from some early Christians whom I think would known better than you or I on the matter.
St. Clement, Letterto the Corinthians, 42, 1 (ANF, Vol. I)
The apostles have preached the Gospel to us from the LordJesus Christ; Jesus Christ [has done so from God. Christtherefore was sent forth by God, and the apostles by Christ. Boththese appointments, then, were made in an orderly way, accordingto the will of God. Having therefore received their orders, andbeing fully assured by the resurrection of our Lord Jesus Christ,and established in the word of God, with full assurance of theHoly Ghost, they went forth proclaiming that the kingdom of Godwas at hand. And thus preaching through countries and cities,they appointed the first-fruits [of their labors], having firstproved them by the Spirit, to be bishops and deacons of those whoshould afterwards believe. Nor was this any new thing, sinceindeed many ages before it was written concerning bishops anddeacons. For thus saith the Scripture a certain place, "Iwill appoint their bishops s in righteousness, and their deaconsin faith."
St. Ignatius of Antioch, Letterto the Magnesians, 6-7 (ANF, Vol., I)
Since therefore I have, in the persons before mentioned,beheld the whole multitude of you in faith and love, I exhort youto study to do all things with a divine harmony, while yourbishop presides in the place of God, and your presbyters in theplace of the assembly of the apostles, along with your deacons,who are most dear to me, and are entrusted with the ministry ofJesus Christ. He, being begotten by the Father before thebeginning of time, was God the Word, the only-begotten Son, andremains the same for ever; for "of His kingdom there shallbe no end," says Daniel the prophet. Let us all thereforelove one another in harmony, and let no one look upon hisneighbor according to the flesh, but in Christ Jesus. Let nothingexist among you which may divide you; but be united with yourbishop, being through him subject to God in Christ.As therefore the Lord does nothing without the Father, forsays He, "I can of mine own self do nothing," so doyou, neither presbyter, nor deacon, nor layman, do anythingwithout the bishop. Nor let anything appear commendable to youwhich is destitute of his approval. For every such thing issinful, and opposed[to the will of] God. Come together into thesame place for prayer. Let there be one common supplication, onemind, one hope, with faith unblameable in Christ Jesus, thanwhich nothing is more excellent. Do you all, as one man, runtogether into the temple of God, as unto one altar, to one JesusChrist, the High Priest of the unbegotten God.
St. Ignatius of Antioch, Letterto the Trallians, 2-3 (ANF, Vol. I)
Be subject to the bishop as to the Lord, for "he watchesfor your souls, as one that shall give account to God."Wherefore also, you appear to me to live not after the manner ofmen, but according to Jesus Christ, who died for us, in orderthat, by believing in His death, you may by baptism be madepartakers of His resurrection. It is therefore necessary,whatsoever things you do, to do nothing without the bishop. Andbe subject also to the presbytery, as to the apostles of JesusChrist, in whom, if we live, we shall [at last] be found.In like manner, let all reverence the deacons as anappointment of Jesus Christ, and the bishop as Jesus Christ, whois the Son of the Father, and the presbyters as the Sanhedrin ofGod, and assembly of the apostles. Apart from these, there is noChurch. Concerning all this, I am persuaded that you are of thesame opinion. For I have received the manifestations of yourlove, and still have it with me, in your bishop, whose veryappearance is highly instructive, and his meekness of itself apower; whom I imagine even the ungodly must reverence.
St. Ignatius of Antioch, Letterto the Philadelphians, 4,1 (ANF, Vol. I)
Wherefore I write boldly to your love, which is worthy of God,and exhort you to have but one faith, and one [kind of]preaching, and one Eucharist. For there is one flesh of the LordJesus Christ; and His blood which was shed for us is one; oneloaf also is broken to all [the communicants], and one cup isdistributed among them all: there is but one altar for the wholeChurch, and one bishop, with the presbytery and deacons, myfellow-servants. Since, also, there is but one unbegotten Being,God, even the Father; and one only-begotten Son, God, the Wordand man; and one Comforter, the Spirit of truth; and also onepreaching, and one faith, and one baptism; and one Church whichthe holy apostles established from one end of the earth to theother by the blood of Christ, and by their own sweat and toil; itbehooves you also, therefore, as "a peculiar people, and aholy nation," to perform all things with harmony in Christ.
St. Ignatius of Antioch, Letterto the Smyrnaeans, 8-9 (ANF, Vol. I)
See that you all follow the bishop, even as Jesus Christ doesthe Father, and the presbytery as you would the apostles; andreverence the deacons, as being the institution of God. Let noman do anything connected with the Church without the bishop. Letthat be deemed a proper Eucharist, which is[administered] eitherby the bishop, or by one to whom he has entrusted it. Whereverthe bishop shall appear, there let the multitude[of the people]also be; even as, wherever Jesus Christ is, there is the CatholicChurch. It is not lawful without the bishop either to baptize orto celebrate a love-feast; but whatsoever he shall approve of,that is also pleasing to God, so that everything that is done maybe secure and valid... It is not lawful without the bishopeither to baptize, or to offer, or to present sacrifice, or tocelebrate a love-feast. But that which seems good to him, is alsowell-pleasing to God, that everything you do may be secure andvalid.And say I, Honor God indeed, as the Author and Lord of allthings, but the bishop as the high-priest, who bears the image ofGod—of God. inasmuch as he is a ruler, and of Christ, in hiscapacity of a priest. After Him, we must also honor the king. Forthere is no one superior to God, or even like to Him, among allthe beings that exist. Nor is there any one in the Church greaterthan the bishop, who ministers as a priest to God for thesalvation of the whole world. Nor, again, is there any one amongrulers to be compared with the king, who secures peace and goodorder to those over whom he rules. He who honors the bishop shallbe honored by God, even as he that dishonors him shall bepunished by God. For if he that rises up against kings is justlyheld worthy of punishment, inasmuch as he dissolves public order,of how much sorer punishment, do you suppose, shall he be thoughtworthy, who presumes to do anything without the bishop, thus bothdestroying the[Church's] unity, and throwing its order intoconfusion? For the priesthood is the very highest point of allgood things among men, against which whosoever is mad enough tostrive, dishonors not man, but God, and Christ Jesus, theFirst-born, and the only High Priest, by nature, of the Father.Let all things therefore be done by you with good order inChrist. Let the laity be subject to the deacons; the deacons tothe presbyters; the presbyters to the bishop; the bishop toChrist, even as He is to the Father.
St. Cyprian of Carthage, Letterwithout heading to the Lapsed (ANF, Vol, V)
Our Lord, whose precepts and admonitions we ought to observe,describing the honor of a bishop and the order of His Church,speaks in the Gospel, and says to Peter: "I say unto you,That you are Peter, and upon this rock will I build my Church;and the gates of hell shall not prevail against it (Matt. 16.18).And I will give unto you the keys of the kingdom of heaven: andwhatsoever you shall bind on earth shall be bound in heaven: andwhatsoever you shall loose on earth shall be loosed inheaven." Thence, through the changes of times andsuccessions, the ordering of bishops and the plan of the Churchflow onwards; so that the Church is founded upon the bishops, andevery act of the Church is controlled by these same rulers.
St. Cyprian of Carthage, EpistleXXXIX, Letter to the People (ANF, Vol, V)
There is one God, and Christ is one, and there is one Church,and one chair founded upon the rock by the word of the Lord.Another altar cannot be constituted nor a new priesthood be made,except the one altar and the one priesthood. Whosoever gatherselsewhere, scatters.
St. Irenaeus, AgainstAll Heresies, IV, 26, 2 (ANF, Vol. I)
Wherefore it is incumbent to obey the presbyters who are inthe Church,—those who, as I have shown, possess the successionfrom the apostles; those who, together with the succession of theepiscopate, have received the certain gift of truth, according tothe good pleasure of the Father. But [it is also incumbent] tohold in suspicion others who depart from the primitivesuccession, and assemble themselves together in any placewhatsoever, [looking upon them] either as heretics of perverseminds, or as schismatics puffed up and self-pleasing, or again ashypocrites, acting thus for the sake of lucre and vainglory. Forall these have fallen from the truth
St. Irenaeus, AgainstAll Heresies, V, 20 (ANF, Vol. I)
It behooves us, therefore, to avoid their doctrines, and totake careful heed lest we suffer any injury from them; but toflee to the Church, and be brought up in her bosom, and benourished with the Lord's Scriptures. For the Church has beenplanted as a garden (paradise) in this world; therefore says theSpirit of God, "You may freely eat from every tree of thegarden," that is, Eat from every Scripture of the Lord; butyou shall not eat with an uplifted mind, nor touch any hereticaldiscord. For these men do profess that they have themselves theknowledge of good and evil; and they set their own impious mindsabove the God who made them. They therefore form opinions on whatis beyond the limits of the understanding. For this cause alsothe apostle says, "Be not wise beyond what it is fitting tobe wise, but be wise prudently," that we be not east forthby eating of the "knowledge" of these men (thatknowledge which knows more than it should do) from the paradiseof life.
Tertullian, PrescriptionAgainst the Heretics, XX, 4 (ANF, Vol. III)
Immediately, therefore, so did the apostles, whom thisdesignation indicates as "the sent." Having, on theauthority of a prophecy, which occurs in a psalm of David, chosenMatthias by lot as the twelfth, into the place of Judas, theyobtained the promised power of the Holy Ghost for the gift ofmiracles and of utterance; and after first bearing witness to thefaith in Jesus Christ throughout Judea, and rounding churches(there), they next went forth into the world and preached thesame doctrine of the same faith to the nations. They then in likemanner rounded churches in every city, from which all the otherchurches, one after another, derived the tradition of the faith,and the seeds of doctrine, and are every day deriving them, thatthey may become churches. Indeed, it is on this account only thatthey will be able to deem themselves apostolic, as being theoffspring of apostolic churches. Every sort of thing mustnecessarily revert to its original for its classification.Therefore the churches, although they are so many and so great,comprise but the one primitive Church, (rounded) by the apostles,from which they all (spring). In this way all are primitive, andall are apostolic, whilst they are all proved to be one, in(unbroken) unity, by their peaceful communion, and title ofbrotherhood, and bond of hospitality,—privileges which no otherrule directs than the one tradition of the selfsame mystery.
St. Augustine: TheHoly Spirit the Soul of the Church (PL 38, Sermo 267; SundaySermons, Vol. III, 27-28)
... What the soul is to the body of man, the Holy Ghost isto the Body of Christ: which the Church is. What the soul does inall the members of one body, this the Holy Spirit does throughoutthe Church ... Do you think the soul follows the part cut thus off? While itbelonged to the body it lived. Cut off it loses life. So likewisethe Christian Catholic man; while in the Body he lives, becomingheretic he is cut off, for the Spirit follows no amputatedmember. If therefore you wish to live in the Holy Ghost, holdfast to the bond of charity, love the Truth, long for Unity, thatyou may attain to eternity.
The discussion as to who the true church actually is, is another conversation for another day I am still waiting for any sort of historical, scriptural, or logical proof that can show that Protestantism is at least a viable option. On the other hand as for your comment on the ranks of the clergy merely being one as elders and the deacon merely being a layman. Again let's look at 1 Timothy 3 to see what St. Paul has to say on the order of bishop, priest, and deacon, the elder being the priest.