In Deuteronomy, after the telling of the ten commandments, the tribal leaders and elders expressed their fears of God and promised to listen and obey God's every command. But God knew they would not always have such hearts. This shows God accepting our promises even when He knows them to be false. God understands us even if we don't fully understand ourselves. We must obey all of God's commands and not stray from His path to lead a long and prosperous life, but we are so weak at the heart and falter from our faith so often, and yet God sticks with us the whole time, because He probably knows that faith will return to us in double-fold in the end.

Psalms 88 is filled with despair and suffering, and calling out to God for mercy and help and yet God turns His face away from him. Why? the psalm does not say. I think it's because he doesn't entirely believe in God and doubt Him so. Even in the psalm he seems to be doubting God with questions, were his faithful cries to God wavering?

Deuteronomy 5:1 and Psalm 88:1