Repentance and Rest are Inseparable (Isaiah 30:15)

"This is what the Sovereign Lord, the Holy One of Israel, says: 'In repentance and rest is your salvation, in quietness and trust is your strength, but you would have none of it'" (Isa 30:15, NIV).

"This is what the Sovereign Lord, the Holy One of Israel, says: 'Only in returning to me and resting in me will you be saved. In quietness and confidence is your strength. But you would have none of it'" (Isa 30:15, NLT).

The Connection between Repentance and Rest (John Oswalt, Isaiah, the NIV Application Commentary, 2003):
Repentance and rest and inseparable (as well as quietness and trust/confidence). God's appeal to his people is "In repentance and rest is your salvation" (Isa 30:15). Both concepts are important, and each is integrally related to the other. There is no real rest (complete dependence on God) without repentance, and there is no real repentance that does not issue in rest.

Repentance is not just to "stop certain sins." The fundamental idea behind repentance in the OT is to turn around or to turn back. It is to stop going in the direction you were, namely, one of self-dependence and self-pleasing, and to turn away from that life to one of depending on God and pleasing him. To talk about resting in the Lord while still keeping hold of one's life and its direction is a contradiction in terms. By the same token, to stop committing certain sins and to "clean up one's act" merely for the sake of avoiding punishment (or to get what we desperately want) is not to turn back to God. It is only to turn away from sin and may be just as selfish as any other act.

Jesus began his ministry with a call for repentance. The NT development of the idea, as expressed in the term metonoia, is the same. To repent is to turn about mentally, spiritually, and behaviorally. How did Jesus begin his ministry? It is by declaring that "the kingdom of God is near." How does one welcome and receive this kingdom? Jesus states that it is by repentance (Mt 4:17; Mk 1:15; Lk 5:32). Unless we repent, i.e., reject the old king--ourselves--and his ways, sin, there is no way we can come into the kingdom of God.

Who is your real king? Just as the OT put the correct relationship with God within the context of absolute loyalty to a covenant king, the NT calls us to turn from loyalty to ourselves and become the glad subjects of heaven's King. If we find real trust difficult, perhaps it is because there has never been a real change of king in our lives. The idea that we can have the benefits of the kingdom without turning away from our own kingship is a fallacy.