The "Paul replaced Judas" theory has been floating around out there for a long time, but it's just a theory. I don't know how anybody could be so dogmatic about this.
As I mentioned, I would respond to this comment. There is no "theory" about Paul being the apostle who replaced Judas. The Bible makes it perfectly clear for those who have spiritual discernment. Here is the evidence:
Why Paul is the 12[SUP]th[/SUP] Apostle
1. The first thing Christians should understand is that there are
only twelve apostles of the Lamb, corresponding to the twelve foundations of the New Jerusalem (Rev 21:14):
And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb.
2. This is further confirmed by the fact that in Christ’s future Kingdom on earth, the twelve apostles will have
twelve thrones and will judge the twelve tribes of Israel (Mt 19:27,28):
Then answered Peter and said unto him, Behold, we have forsaken all, and followed thee; what shall we have therefore? And Jesus said unto them, Verily I say unto you, That ye which have followed me, in the regeneration when the Son of man shall sit in the throne of his glory, ye also shall sit upon twelve thrones, judging the twelve tribes of Israel.
3. Judas was never a genuine apostle, betrayed Christ, and vacated his apostleship. He was chosen in order to fulfil the prophecies regarding the betrayal of Christ (Acts 1:16):
Men and brethren, this scripture must needs have been fulfilled, which the Holy Ghost by the mouth of David spake before concerning Judas, which was guide to them that took Jesus.
4. The remaining eleven apostles had not been empowered by the Holy Spirit at the time that they decided to cast lots for a fill-in for Judas (Acts 1:4):
And, being assembled together with them, [Christ] commanded them that they should not depart from Jerusalem, but wait for the promise of the Father, which, saith he, ye have heard of me. They were supposed to wait until the day of Pentecost, which would be ten days later. So this was not a commissioning of the 12[SUP]th[/SUP] apostle by Christ Himself, although He allowed this.
5. There were two men who were potential candidates, and it was only by lot that Matthias came to be chosen (Acts 1:26):
And they gave forth their lots; and the lot fell upon Matthias; and he was numbered with the eleven apostles.
It should be carefully noted that after this Matthias is ABSENT from the New Testament record, whereas Paul dominates the Acts of the Apostles and writes over half the New Testament Scriptures! And there cannot be 13 apostles!
6. God already had another plan to complete the number of apostles, and He had chosen Paul (formerly Saul) from his mother’s womb (Gal 1:15,16):
But when it pleased God, who separated me from my mother's womb, and called me by his grace, To reveal his Son in me, that I might preach him among the heathen; immediately I conferred not with flesh and blood:
This is a very powerful statement, which is generally ignored by the naysayers. If God had chosen this man to be an apostle even before he was born, how dare anyone deny the fact that he is the 12[SUP]th[/SUP] apostle?
7. Because of this the Lord Jesus Christ appeared to Paul personally while he was traveling to Damascus, and converted him from Saul the persecutor of Christians to Paul His faithful apostle. The account of Saul’s conversion is in Acts 8:1-31 and Acts 22:1-21, but the details of his commissioning as an apostle are given in Acts 26:14-18:
And when we were all fallen to the earth, I heard a voice speaking unto me, and saying in the Hebrew tongue, Saul, Saul, why persecutest thou me? it is hard for thee to kick against the pricks. And I said, Who art thou, Lord? And he said, I am Jesus whom thou persecutest. But rise, and stand upon thy feet: for I have appeared unto thee for this purpose, to make thee a minister and a witness both of these things which thou hast seen, and of those things in the which I will appear unto thee; Delivering thee from the people, and from the Gentiles, unto whom now I send thee, To open their eyes, and to turn them from darkness to light, and from the power of Satan unto God, that they may receive forgiveness of sins, and inheritance among them which are sanctified by faith that is in me.
8. The apostle Peter has confirmed that
all of Paul’s epistles are Scripture (2 Pet 3:15,16). Therefore each time we read one of his epistles, we are reading the Word of God – God’s words.
And it is through the words of God that we are told again and again that Paul is the 12[SUP]th[/SUP] apostle:
Paul, a servant of Jesus Christ, called [to be] an apostle, separated unto the gospel of God (Rom 1:1)
Paul, called [to be] an apostle of Jesus Christ through the will of God, and Sosthenes [our] brother (1 Cor 1:1)
Paul, an apostle of Jesus Christ by the will of God, and Timothy [our] brother, unto the church of God which is at Corinth, with all the saints which are in all Achaia (2 Cor 1:1)
Paul, an apostle, (not of men, neither by man, but by Jesus Christ, and God the Father, who raised him from the dead (Gal 1:1)
Paul, an apostle of Jesus Christ by the will of God, to the saints which are at Ephesus, and to the faithful in Christ Jesus (Eph 1:1)
Paul, an apostle of Jesus Christ by the will of God, and Timotheus [our] brother (Col 1:1)
Paul, an apostle of Jesus Christ by the commandment of God our Saviour, and Lord Jesus Christ, [which] is our hope (1 Tim 1:1)
Paul, an apostle of Jesus Christ by the will of God, according to the promise of life which is in Christ Jesus (2 Tim 1:1)
Paul, a servant of God, and an apostle of Jesus Christ, according to the faith of God's elect, and the acknowledging of the truth which is after godliness (Tit 1:1)
If all of this is not enough to establish that Paul is indeed the 12[SUP]th[/SUP] apostle of Jesus Christ, then nothing is. Those who will acknowledge the truth will accept this. Those who will not choose to be wilfully blind, and there is no remedy for that.