“Take care, brothers, that none of you may have an evil, unbelieving (Gk. apistia) heart that turns away from the living God (3:12)…So we see that they [the Hebrews] were unable to enter [into rest] because of unbelief (Gk. apistia, 3:19).”
Several features of this text are relevant to the role of unbelief and its relationship to falling away.
As in Romans 11, the unbelief of the Hebrew people is the basis of the exhortation to the Christian community to persevere in faith. This means that multiple New Testament authors saw Israel’s unbelief as analogous to the potential situation in which Christians might fall into unbelief. It may also suggest continuity between the Old Testament people of God and the New Testament people of God, since the new are liable to the same danger as the old.
The passage is directly addressed to the Christian community and presupposes belief in the God revealed in Jesus. The explicit addressees are “brothers”, a common descriptor for members of the visible community of believers in the early Christian movement. In 3:1, the term “brothers” is qualified by the phrase “holy partners in a heavenly calling”, which emphasizes the author’s understanding that they are true believers. The addressees are warned not to turn away from God, which suggests that they are presently oriented toward God in contrast to those who are rebellious.
Turning away from God is directly correlated with an unbelieving heart (apistia). This suggests that the author saw it as a real possibility that believing Christians might return to unbelief and turn from God, thus falling away from membership in the people of God and falling away from participation in the saving work of God; thus jeopardizing their entrance into God’s rest.