Who sustains our salvation?

Let's look at Colossians 1:23:

IF indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard, which has been proclaimed in all creation under heaven, and of which I, Paul, became a minister.

Here the translations start off with a conditional "if indeed" (eige/G1489)

However the Greek word has within its range of meaning "since." Thus the verse could be translated as "Since you are persisting in the faith..." This view asks the question, "Since what" and the answer is "being reconciled to God."

Thus the proof of being reconciled is persisting in the faith and not shifting from the hope of the gospel! Our eternal security is provided by God protecting our credited faith, so we are unable to not persist if we are born anew.

 

Hebrews 12:1b-2 (NASB)
let’s run with endurance the race that is set before us, looking only at Jesus, the originator and perfecter of the faith, who for the joy set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God.

The Greek word translated "originator" is also translated as "author" and refers to the One who provides the initial basis for "the faith." The Greek word translated "perfecter" is also translated "completer or finisher" of the faith, and refers to the fact Christ provides everything of which "the faith" is comprised. As with Alpha and Omega, Christ is both the initiator and completed embodiment of "the faith."