A.T. Robertson Commentary Hebrews 3:14

"for we are become partakers of Christ, if we hold fast the beginning of our confidence firm unto the end:" — Hebrews 3:14 (ASV)

For we are become partakers of Christ (μετοχο γαρ του Χριστου γεγοναμεν). Second perfect active of γινομα, "we have become," not the equivalent of εσμεν (are). For μετοχο see 1:9; 3:1; 6:4. We have become partners with Christ and hence (γαρ, for) should not be tricked into apostasy.

If we hold fast (εαν περ κατασχωμεν). The same condition as in verse 6 with περ (indeed, forsooth) added to εαν. Jonathan Edwards once said that the sure proof of election is that one holds out to the end.

The beginning of our confidence (την αρχην της υποστασεως). For υποστασις see 1:3; 11:1. These faltering believers (some even apostates) began with loud confidence and profession of loyalty. And now?