What does Hebrews 3:19 mean?

This is the last of the four ways in which spiritual failure can cause us to miss out on blessings from God. The context is that of Israel and her wandering in the desert. Despite common use, the Promised Land is not meant to be a symbol of heaven in the Bible—there was still war, work, and strife in Canaan. Salvation, in the story of Israel, was her liberation from Egypt. God did not send the rebellious people back to slavery. He will not let a saved Christian fall into eternal damnation. However, He will discipline a Christian who exhibits spiritual failures with a loss of their spiritual inheritance.

Prior verses used the example of Israel to point out the errors of rebellion, sin, and defiance. Here, "faithlessness" is mentioned. This is from the Greek term apistian. As used in the Bible, it is applied to those who lack faith entirely, those who have a weak trust in God, and those who fail to maintain trust. When Israel saw the "giants" of Canaan, they "chickened out" on God, and demonstrated this kind of "unbelief."

Hebrews was originally written to Jewish Christians suffering under persecution. There would have been a strong temptation to "chicken out" and revert back to Judaism, or otherwise compromise their faith. However, this apistian risks discipline from God. The spiritual inheritance we are promised—something separate from our eternally secure salvation—is contingent on our being willing to "hold fast" to our faith (Hebrews 3:6). Faithlessness makes pleasing God impossible (Hebrews 11:6).