This is an ancient debate. Catholics believe you choose God’s merciful grace through free will, through not only a declaration, but also through chosen thoughts and actions (via free will) constantly. This battle to overcome human frailties is overcome by God, theologically - but there is still a human step needed, almost constantly, to accept, which, again, is manifest in thoughts and actions. And so we pray for God to give us and others the knowledge and strength to make that step. How is that different than the basic Protestant teaching?
The way you are perceiving the issue of 'getting saved, then retaining that salvation' is in fact the way you excuse your 'striving for salvation' ... you remain caught in the works based salvation, stealthily hiding your pride in works as the notion of you must keep your salvation, as if GOD plays yo-yo with your immortal soul by depositing Life in your dead spirit then snatching it away when you fail to perform as your religion has misguided you to believe you must behave.
You religion has taken Pauls advice to 'work out your own salvation' to mean something Paul did not intend as proven by the rest of his instructions to us. Salvation is a gift of GOD to the one who believes God's Promise to regenerate that one. Your religion has added 'now you must take responsibility to keep that gift or God will take it away, but might give it back if you do what the orh instructs you to do.
THAT is not salvation by Grace, it is salvation by your mighty effort. And yes, if you could do it that would be mighty since an intellect far beyond yours is constantly tempting you to violate a law which has been dealt with In CHRIST once for all forever.
Will you learn what it means to be a new creation, alive in the now, even as the dead old man remains in the wings, stinking up the place?