I know that idea is common amongst Calvinists, but I don't believe that is the correct interpretation of Ephesians 2:8. No, faith isn't the gift... the Holy Spirit and Salvation are the gift. Faith is how we become qualified for human adoption and thereby qualified as heirs. When we have the same faith in the gospel that Abraham had we are considered the descendants of Abraham.
[Gal 3:14 NASB] 14 in order that in Christ Jesus the blessing of Abraham might come to the Gentiles, so that we would receive the promise of the Spirit through faith.
[Eph 1:13-14 NASB] 13 In Him, you also, after listening to the message of truth, the gospel of your salvation--having also believed, you were sealed in Him with the Holy Spirit of promise, 14 who is given as a pledge of our inheritance, with a view to the redemption of [God's own] possession, to the praise of His glory.
[Rom 4:11] 11 and he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be the father of all who believe without being circumcised, that righteousness might be credited to them,
[Rom 2:28-29 NASB] 28 For he is not a Jew who is one outwardly, nor is circumcision that which is outward in the flesh. 29 But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter; and his praise is not from men, but from God.
In the pattern of Abraham, the archetype for faith, we see that he believed and then was sealed with circumcision. Circumcision is Old Testament foreshadow for the indwelling of the Holy Spirit. The context of Ephesians 2:8 is Ephesians 1:13 which says that the indwelling of the Holy Spirit comes AFTER faith, not before faith. Romans 2:28-29 says that the Holy Spirit in us is "circumcision of the heart." Galatians 3:14 says that we receive the promise of the spirit through faith.... not faith through the promise of the Spirit. So the gift is the Holy Spirit, not faith.
Further, that in Romans 4 we are told repeatedly that Abraham was made righteous for his faith WHILE uncircumcised (or prior to being indwelled with the Holy Spirit in New Testament vernacular).
[Rom 4:9-17 NASB] 9 Is this blessing then on the circumcised, or on the uncircumcised also? For we say, "FAITH WAS CREDITED TO ABRAHAM AS RIGHTEOUSNESS." 10 How then was it credited? While he was circumcised, or uncircumcised? Not while circumcised, but while uncircumcised; 11 and he received the sign of circumcision, a seal of the righteousness of the faith which he had while uncircumcised, so that he might be the father of all who believe without being circumcised, that righteousness might be credited to them, 12 and the father of circumcision to those who not only are of the circumcision, but who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. 13 For the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith. 14 For if those who are of the Law are heirs, faith is made void and the promise is nullified; 15 for the Law brings about wrath, but where there is no law, there also is no violation.16 For this reason [it is] by faith, in order that [it may be] in accordance with grace, so that the promise will be guaranteed to all the descendants, not only to those who are of the Law, but also to those who are of the faith of Abraham, who is the father of us all, 17 (as it is written, "A FATHER OF MANY NATIONS HAVE I MADE YOU") in the presence of Him whom he believed, [even] God, who gives life to the dead and calls into being that which does not exist.
So we see here in Romans 4:16 the echoing of what is stated in Ephesians 2:8 but without the possibility of confusing faith as the gift. Here, we see that righteousness is the gift.
[Rom 5:17 NASB] 17 For if by the transgression of the one, death reigned through the one, much more those who receive the abundance of grace and of the gift of righteousness will reign in life through the One, Jesus Christ.
Since death came by sin, reason tells us that life comes by righteousness. The Bible even seems to use life and righteousness as synonymous.
[Gal 3:21 NASB] 21 Is the Law then contrary to the promises of God? May it never be! For if a law had been given which was able to impart life, then righteousness would indeed have been based on law.
Righteousness and life are the definition of salvation.
[Rom 5:10 NASB] 10 For if while we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life.
So when Ephesians 2:8 says "we are saved by grace through faith; it is the gift of God" we know that righteousness and the Holy Spirit are life, and that life is our salvation. So the "gift" from Ephesians 2:8 is not faith, but rather being "saved" is the gift.
If I said "
You are given cash by compassion through electronic transfer. This gift is from me." we would know that "cash" is the gift, not "electronic transfer". Electronic transfer is HOW the gift of cash arrived... it is not the gift itself. The sentence structure is the same in Ephesians 2:8.