Let's select "the faithfulness of Christ" for the moment;
Now let's read the verse... but wait[!]... first we must place back into that verse a very vital phrase for its "making sense". (It doesn't make sense the way you had written it without that phrase, yeah, but if one INCLUDES that vital phrase that you'd left out, it DOES straighten out the "sense" of it, and aids our understanding of what it is conveying).
I'll ask you. What "phrase" am I referring to that you've "left out" of verse 22.
Then (once you re-insert the words that also belong in that verse), read the sentence with the quoted red words from your options, the one I suggested we should select for the moment, to read the ENTIRE verse (nothing left out) using that particular suggested option.
faith in Jesus Christ -- Three times in this verse Paul declares that salvation is only through faith in Christ and not by law. The first is general, “a man is not justified”; the second is personal, “we might be justified”; and the third is universal, “no flesh shall be justified.” - MSB
through faith of Christ -- dia pisteos Christou, διὰ πίστεως Ἰησοῦ Χριστοῦ, "The words "the faith of Christ" have been variously understood. One group takes it to refer to our faith in Christ; another group takes it to refer to the gospel thus the objective faith of Christ. On the whole it seems more probable that in this context it refers to the gospel." - Noel Merideth
faith in Jesus Christ. -- Some believe that the reference is to the “faithfulness of Jesus Christ.”
Lightfoot, however, observes, “Faith is, strictly speaking, only the means, not the source of justification. - PC
διὸ πίστεως Χρ. Ἰης., “by means of faith in Christ Jesus.”
καὶ ἡμεῖς, “even we” with all our privileges, taking up the ἡμεῖς of Gal_2:15.
εἰς Χρ. Ἰης. ἐπιστεύσαμεν. πιστεύω εἰς, though common in St John’s writings, occurs in St Paul’s only here and Rom_10:14, Php_1:29. It has, as it seems, with him the same strong sense as with St John,
to cease to lean on oneself and to place one’s entire trust on Christ. Observe the “ingressive” aorist, like ἐβασίλευσε … Γύγης, Gyges became king, Herodot. I. 13 (Gildersleeve, § 239).
ἴνα δικαιωθῶμεν ἐκ πίστεως Χριστοῦ. ἐκ is stronger than the preceding διά, and excludes all sources of justification other than faith on Christ.
The omission of Ἰησοῦ may be due only to a wish to avoid repetition, but perhaps to a desire to emphasize the thought that a true Jew finds his justification in Messiah. Cf. Gal_2:4 note on ἐν Χρ. Ἰης.
but by the faith of Jesus Christ; not by that faith, which Christ, as man, had in God, who promised him help, succour, and assistance, and for which he, as man, trusted in him, and exercised faith upon him;
but that faith of which he is the object, author, and finisher; and not by that as a cause, for faith has no causal influence on the justification of a sinner; it is not the efficient cause, for it is God that justifies; nor the moving cause, or which induces God to justify any, for that is his own free grace and good will; nor the meritorious or procuring cause, for that is the obedience and bloodshed of Christ; nor is faith the matter of justification; it is not a justifying righteousness; it is a part of sanctification; it is imperfect; as an act it is a man's own, and will not continue for ever in its present form, nature, and use; and is always distinguished from the righteousness of God, by which we are justified, which is perfect, is another's, and will last for ever. Men are not justified by faith, either as an habit, or an act; not by it as an habit or principle, this would be to confound justification and sanctification; nor as an act, for as such it is a man's own, and then justification would be by a man's works, contrary to the Scripture:
but faith is to be taken either objectively, as it relates to Christ, the object of it, and his justifying righteousness; or as it is a means of receiving and apprehending Christ's righteousness; the discovery of it is made to faith; that grace discerns the excellency and suitableness of it, approves of it, rejects a man's own, lays hold on this, and rejoices in it:
Gill
J.