18 And to whom did He swear that they would not enter His rest, but to those who did not obey?
The “and” here continues the grounds for exhortation in Hebrews 3:15.
to whom did He swear that they would not enter His rest,
Those who did not enter the Promised Land are those who rebelled against God’s oath. This is the second reference to God’s oath about His prohibition of some in Israel not going into the land (He 3:11). He will refer to His oath about this again in Hebrews 4:3.
The rest here is rest in Christ.
but to those who did not obey?
Israel disobeyed God in Numbers 14:22-23 by their complaints. To not obey is to not apply to experience what God has to say.
Unbelief leads to disobedience.
Unbelief leads to disobedience and disobedience leads to spiritual failure. Spiritual failure results in loss of entering God’s “rest.” Not only do many of those who rebel against the Lord experience an early death but tragically they do not come to the place of enjoying the benefits of the Christian life. Unbelief is at the root of this failure.
Most of the Israelites who came out of Egypt and died in the desert were believers (Ex 14:31). They died as believers and did not lose their eternal salvation. However, they lost what would have been their blessings.