Psalm 78:36-37 Nevertheless they did flatter him with their mouth, and they lied unto him with their tongues. For their heart was not right with him, neither were they stedfast in his covenant.
The hypocrite responds to the Lord by flattering and lying with their tongues, while their hearts are far from Him. Their heart was not right with God, nor were they faithful to His covenant. This is the classic hypocrite that Jesus excoriates in the NT.
We, as outwardly religious people, learn to worship and say the right things, but the heart is not in agreement. We are not steadfast in the covenant He made with us by breaking the Commandments to love God and love neighbor. Yet we know how to act pious for show even though the heart is not right.
God loves the heart that is right with Him through a God-wrought faith in Jesus through the Gospel. The tongue will honestly follow a heart that is cleansed, forgiven and right with God. We are not steadfast in His covenant, but Jesus is. Through the shed blood of Christ God makes a New Covenant with us. When we repent of our own works and believe the gospel our tongue matches our heart. We are still lying hypocrites, but the Spirit is in the process of sanctification by bringing our tongue in line with our heart. Daily repentance, confession, faith and remembrance of Baptism prevents hypocrisy.