What does Hebrews 10:23 mean?

The book of Hebrews was originally written to Jewish Christians who were experiencing persecution. They were under pressure to return to a more popular, easier religion. Namely, Judaism. Much of the letter, to this point, has been explaining reasons to be confident that Jesus Christ, not the old covenant priesthood, is God's ultimate plan for mankind's salvation. Part of the encouragement to "hold fast" given here comes from that perspective (Hebrews 3:14). Christ is the fulfillment of God's will for mankind, so we should resist the pressures of anything which tries to take us away from Him.

At the same time, this statement comes in the context of several warnings. The writer of Hebrews has cautioned the reader about the dangers of being careless, shallow, or dismissive of their Christian faith (Hebrews 2:1–4; 6:1–8). A prominent example is given in chapter 3, regarding Israel's failure in the desert, at the borders of the Promised Land (Hebrews 3:12–19). There, Israel succumbed to fear and doubt, and did not "hold fast" to their trusting faith in God. Christians are called not to make this mistake. Instead, we should embrace the confidence we have in Christ, and His salvation, and act accordingly.