Faith is not a pre-requisite of salvation....nothing that we as men can contribute, is.
As for crediting a person's faith as righteousness, He is pleased to do so;
not as a necessity, but as an act of His grace and mercy towards His people...
People like Abraham, Isaac, Jacob, David, Mary, Miriam, Esther and so forth.
The only righteousness that the believer has, is from Jesus Christ.
There is no other righteousness, only God's righteousness.
Nothing that we as believers have or do is righteous in and of itself;
Not our faith, not our works, nothing.
Everything we have or do is because of Him and Him alone:
"But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets;
even the righteousness of God [which is] by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
for all have sinned, and come short of the glory of God;
being justified freely by his grace through the redemption that is in Christ Jesus:
whom God hath set forth [to be] a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God;
to declare, [I say], at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus." ( Romans 3:21-26 ).
" For if by one man’s offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.) Therefore as by the offence of one [judgment came] upon all men to condemnation; even so by the righteousness of one [the free gift came] upon all men unto justification of life.
For as by one man’s disobedience many were made sinners, so by the obedience of one shall many be made righteous.
Moreover the law entered, that the offence might abound.
But where sin abounded, grace did much more abound:
that as sin hath reigned unto death, even so might grace reign through righteousness unto eternal life by Jesus Christ our Lord." ( Romans 5:17-21 ).
" But what things were gain to me, those I counted loss for Christ.
Yea doubtless, and I count all things [but] loss for the excellency of the knowledge of Christ Jesus my Lord: for whom I have suffered the loss of all things, and do count them [but] dung, that I may win Christ,
and be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:" ( Philippians 3:7-9 ).
The only faith a believer has, is from Jesus Christ ( Romans 3:22, Galatians 2:20, Galatians 3:22, Philippians 3:9, Hebrews 12:2 )
" For I through the law am dead to the law, that I might live unto God.
I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain."