We cannot boast because we cannot secure our own salvation, believing/faith is not a work and it the same for everyone no does less or more to receive the gift therefore there is no boasting.
I find it interesting that faith in the Catholic tradition faith is given/infused by God to the person, this concept permeates their doctrine.
From a Greek scholar who I think is unbiased.
A.T. Robertson states: And that (kai touto). Neuter, not feminine tautē, and so refers not to pistis (feminine) or to charis (feminine also), but to the act of being saved by grace conditioned on faith on our part. Paul shows
that salvation does not have its source (ex humōn, out of you) in men, but from God. Besides, it is God's gift (dōron) and not the result of our work.
This verse in Ephesians makes it clear that it is the person who believed.
Ephesians 1:13
In Him
you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also,
having believed, you were sealed with the Holy Spirit of promise,
Also from notes although I do not have the citation,
Aside from the interpretive possibility of
Ephesians 2:8, there seems scant biblical evidence that "faith" is a gift from God. When Paul holds up Abraham as an example of faith, he esteems Abraham’s personal and self generated faith. In another example where Jesus is conversing with Martha (
John 11:25-27), Martha demonstrates a self generated belief of something that was true (Jesus as the Messiah).
Interestingly enough there is evidence Calvin did not consider faith the gift in Ephesians 2:8 although I have researched this so I cannot say with certainty.
Aside from this though, what Ralphie is stating that initial faith is a gift and then we have to maintain that gift of faith to be saved makes no sense.