Psalm 78:10-11 They kept not the covenant of God, and refused to walk in his law; and forgot his works, and his wonders that he had shewed rhem.
Instead of responding to God’s great works of salvation with faith and obedient thanksgiving, the people disobeyed God and did not keep His covenant. Instead of remembering God’s work, His people forgot God and lived their own way.
It seems amazing that the delivered people would so soon forget God and His wonderful works of salvation, but it reveals to us just how sinful and depraved we are as sinners. The warning is meant for us that we might daily and weekly remember how rotten and corrupt we are. And we need constant reminders of the amazing grace, the undeserved mercy, and the unconditional love of God given to us in the Gospel of Christ.
The cross is to be always and ever before our eyes that we might remember God and His work of salvation at the cross and live a life of faith.