Those Hebrews passages - again - do not refer to salvation. Matters not if the TERM is not in Scripture. It’s clear from the passages and AFTER that the author is NOT referencing those who are saved/redeemed (if you prefer). We cannot keep ourselves. Yes, we have a responsibility to follow Him. Just like we are commanded to “Repent and Believe”, although Scripture makes it clear that salvation is of the Lord and NO ONE seeks after God, no not one (Romans 3),
Philippians 1:6 shows who keeps us, as does John 6 (v. 39) and John 10:28-29 (and I give eternal life to them, and they will never perish; and no one will snatch them out of My hand. 29 [a]My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of the Fathers hand.). Romans 5 - “....having now been justified” (eternity past). Josh Harris is not more powerful than the Savior who keeps us, God be praised.
1 John 2:19 “They went out from us, but they were not really of us; for if they had been of us, they would have remained with us; but they went out, so that [d]it would be shown that they all are not of us.”