Romans 12 is written to believers, those who are already in the body of Christ.
Rom 12:1 I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.
2 And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
3 For I say, through the grace given unto me, to every man that is among you, not to think of himself more highly than he ought to think; but to think soberly, according as God hath dealt to every man the measure of faith.
4 For as we have many members in one body, and all members have not the same office:
5 So we, being many, are one body in Christ, and every one members one of another.
6 Having then gifts differing according to the grace that is given to us, whether prophecy, let us prophesy according to the proportion of faith;
These are spiritual gifts given, especially to the early Church, they included performing miracles, speaking in tongues, healing and other gifts. And not every person was given the same gift. If this was speaking of unbelievers, then all would be saved, because verse 3 says God hath dealt to "every man" the measure of faith. All would have faith in Christ, and all would be saved.
1 Cor 12:1 Now concerning spiritual gifts, brethren, I would not have you ignorant.
2 Ye know that ye were Gentiles, carried away unto these dumb idols, even as ye were led.
3 Wherefore I give you to understand, that no man speaking by the Spirit of God calleth Jesus accursed: and that no man can say that Jesus is the Lord, but by the Holy Ghost.
4 Now there are diversities of gifts, but the same Spirit.
5 And there are differences of administrations, but the same Lord.
6 And there are diversities of operations, but it is the same God which worketh all in all.
7 But the manifestation of the Spirit is given to every man to profit withal.
8 For to one is given by the Spirit the word of wisdom; to another the word of knowledge by the same Spirit;
9 To another faith by the same Spirit; to another the gifts of healing by the same Spirit;
10 To another the working of miracles; to another prophecy; to another discerning of spirits; to another divers kinds of tongues; to another the interpretation of tongues:
11 But all these worketh that one and the selfsame Spirit, dividing to every man severally as he will.
12 For as the body is one, and hath many members, and all the members of that one body, being many, are one body: so also is Christ.
Verse 9 says to one believer is given faith. It does not say all are given faith. This was a special gift. Paul says more about this in the very next chapter. And if you interpret this to mean the faith to believe in Christ, then all men would be saved because verse 7 says the manifestation of the Spirit is given to "every man". So all men would receive the gift of the Holy Spirit and be saved.
1 Cor 13:2 And though I have the gift of prophecy, and understand all mysteries, and all knowledge; and though I have all faith, so that I could remove mountains, and have not charity, I am nothing.
Let me ask you this, have you removed any mountains lately? I know I haven't. And I haven't performed any miracles or healed anyone either.
These were special gifts given to the early church especially to further the gospel. There is really no record of the gifts continuing after the 1st century, although some believe they continue today.
So, this is not speaking of the faith to receive and accept Jesus as your saviour, this was a spiritual gift given to those who already believe to perform supernatural works.
You can't pull verses out of context to prove your doctrine.