I think you've misunderstood the noun for "faith". It's not our action that keeps us saved. The word "faith" is a noun, and means God's Word, which is what we believe. God's Word is what keeps us saved, by grace.
As to what keeps us "for the day of salvation", Paul said it this way:
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 Eph 1:13
Then, Paul said this:
Do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.
So, having believed, we are sealed with the Holy Spirit "in Him". And we were sealed FOR THE DAY OF REDEMPTION.
I find it informative that Paul even included the problem of grieving the Holy Spirit. In spite of doing that, we are STILL sealed FOR THE DAY OF REDEMPTION.
Seems according to the 'loss of salvation' crowd, if one grieves the Holy Spirit, they lose salvation.
Clearly, they do not.