You are in error.
You are disconnecting "salvation" from being a manifest state inclusive of heart purity having been set free from every lawless deed, and are instead viewing salvation as an "abstract position."
I'll break it down for you.
You say this...
"but his walk in faith doesn't grow, and he decides to deny Christ."
Thus you have an individual who is in a "present state" of having "decided to deny Christ" and is thus clearly "not WALKING adding to their faith." Yet you connect that present reality to "could end up with loss of salvation." You are viewing "salvation" as a POSITION they hold as opposed to a tangible reality reflective of the condition of one's soul and character.
Salvation is a manifest state of being alive to God through the Spirit, it is not a position one holds.
Look at what the Bible states...
Tit 2:14 Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works.
Jesus gave Himself for us for the express purpose of...
1. Redeeming us from ALL iniquity.
2. Purifying unto Himself a peculiar people.
Redeem means...
Redeem - lutroō
From G3083; to ransom (literally or figuratively): - redeem.
G3083 lutron
From G3089; something to loosen with, that is, a redemption price (figuratively atonement): - ransom.
G3809 luō
A primary verb; to “loosen” (literally or figuratively): - break (up), destroy, dissolve, (un-) loose, melt, put off. Compare G4486.
What is one "loosened" or "put off" from?
"he might redeem us from all iniquity" (Tit 2:14).
Compare to...
Rom 6:16 Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?
Rom 6:17 But God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you.
Rom 6:18 Being then made free from sin, ye became the servants of righteousness.
See how Paul recognises a "service" to either unrighteousness or righteousness?
There are two kinds of people alluded to in Romans 6:16.
1. Servants of Sin - Servants of Unrighteousness
2. Servants of Righteousness - Those Whom Obey From the Heart
Now look back at Titus 2:14 and you'll see it says...
"he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works."
There is an association between being set free from ALL iniquity and being both pure and zealous for righteousness. Now look at what Jesus taught...
Mat 7:21 Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
Mat 7:22 Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
Mat 7:23 And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
Mat 7:24 Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock:
Mat 7:25 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell not: for it was founded upon a rock.
Mat 7:26 And every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand:
Mat 7:27 And the rain descended, and the floods came, and the winds blew, and beat upon that house; and it fell: and great was the fall of it.
Jesus speaks of two kinds of people...
1. Workers of iniquity - Those whom do not DO the will of the Father.
2. Hearers and Doers - Those whom do the will of the Father.
One kind of people is still "serving sin" whilst the other kind of person is "serving righteousness."
Compare to what John wrote...
1Jn 3:7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.
1Jn 3:8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
1Jn 3:9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
1Jn 3:10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
John warned to not let ANYONE deceive you. He that DOES what is righteous is righteous even as Jesus Christ is righteous.
The word for DOETH and COMMIT is "poieō" in the Greek and it means PRODUCE or BRING FORTH. It is the "deeds" or "action" produced by an individual.
The children of God are MANIFEST (made known) in that they do not produce the deeds of unrighteousness in their lives because the seed of Jesus Christ is present within them. One cannot be "abiding in Jesus" and be "working iniquity" at the same time.
Jesus prayed...
Joh 17:22 And the glory which thou gavest me I have given them; that they may be one, even as we are one:
Joh 17:23 I in them, and thou in me, that they may be made perfect in one; and that the world may know that thou hast sent me, and hast loved them, as thou hast loved me.
Salvation is a MANIFEST STATE of being one in Christ, the love of God having been shed abroad in the heart (Rom 5:5) via the washing of regeneration by the Holy Ghost (Tit 3:5). Anyone without a testimony of truly being delivered from "working iniquity" and "purified" whereby they are zealous for righteousness is not saved.
Satan has deceived multitudes of religious people who call themselves Christian's into believing in a salvation which is PURELY POSITIONAL apart from an actual total transformation of their heart. Paul wrote...
2Co 5:17 Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new.
To be IN CHRIST is a present manifest reality of WALKING IN THE SPIRIT by which the RIGHTEOUSNESS OF GOD is literally fulfilled within the heart and thus that which is PRODUCED OUTWARDLY is righteousness. There is no condemnation upon those whom are alive in this present manifest state for they are walking according to the Spirit and are in union with Jesus Christ, He in them, and they in Him, being perfect in one...
Rom 8:1 There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
Rom 8:2 For the law of the Spirit of life in Christ Jesus hath made me free from the law of sin and death.
Rom 8:3 For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh:
Rom 8:4 That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.
Here is a video I made which explains these things in a very clear manner, please take a look.
[video=youtube;4EZp0tvX1tQ]https://www.youtube.com/watch?v=4EZp0tvX1tQ[/video]
I would ignore the "servants of sin" whom pervade these forums. Arguing with them is pointless, they generally spend an inordinate amount of their time on an internet forum soothing their conscience of the reality of a SALVATION POSITION (sporting their own deceivings) whilst they still remain literal slaves of corruption...
2Pe 2:10 But chiefly them that walk after the flesh in the lust of uncleanness, and despise government. Presumptuous are they, selfwilled, they are not afraid to speak evil of dignities.
2Pe 2:11 Whereas angels, which are greater in power and might, bring not railing accusation against them before the Lord.
2Pe 2:12 But these, as natural brute beasts, made to be taken and destroyed, speak evil of the things that they understand not; and shall utterly perish in their own corruption;
2Pe 2:13 And shall receive the reward of unrighteousness, as they that count it pleasure to riot in the day time. Spots they are and blemishes, sporting themselves with their own deceivings while they feast with you;
2Pe 2:14 Having eyes full of adultery, and that cannot cease from sin; beguiling unstable souls: an heart they have exercised with covetous practices; cursed children: