Belief comes first. Even we have believed in Jesus Christ. Why? That we might be justified by the faith of Jesus Christ. God’s righteousness is by faith of Jesus Christ. It’s s unto all and upon all them that believe, Jew or Gentile.
Romans 3:
21 But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets;
22 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:
Righteousness of God is by the faith of Christ. The "upon all them that believe" is referencing that the "righteousness of God" as being that which is upon them, not because they believed did they receive the righteousness of God. Their belief in Christ is the fruit and the earnest, of the righteousness of God having been given to them. Their belief in Christ came after, or from, the righteousness of God, it is not for the righteousness of God.
[2Th 2:13-14 KJV] 13 But we are bound to give thanks alway to God for you, brethren beloved of the Lord, because
God hath from the beginning
chosen you to salvation through sanctification of the Spirit and belief of the truth:
[1Pe 1:21 KJV] 21
Who by him do believe in God, that raised him up from the dead, and gave him glory; that your faith and hope might be in God.
[Gal 2:16 KJV] 16 Knowing that a man is not justified by the works of the law,
but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
[Gal 5:22 KJV] 22
But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness,
faith,