But then they would flatter Him with their mouths, lying to Him with their tongues; their hearts were not loyal to Him, they were not faithful to His covenant.
Psalm 78:36-37 (NIV)
Some people struggling with sin always find themselves faced with two situations. They either choose to renounce sin completely to seek God's face and align themselves with His word, or they pretend to renounce it by finding a reason to delve into it another time. In the second case, when they abandon sin, it is always following a horrible consequence that causes fear and embarrassment.
The consequences of their sin will awaken their conscience and motivate them to fight a temporary battle until the storm subsides. They will hate sin so much that they will put all their strength into it to escape it and please God. Their hearts being insincere and their repentance in vain, they will fall prey to the same sin that caused them to seek God's forgiveness.
It is the same situation with the people of Israel. They sinned against God and because He opposed them, they repented but their repentance was not sincere and their hearts were not faithful to His covenant. God offers you the opportunity to be in agreement with Him. His forgiveness is always available but our confession must be made with remorse and regret, this is the only way our prayers will be heard and answered.