Contradiction with Matthew 7:21
Zechariah 6:15 suggests that obedience to God's commands leads to relationship with Him, whereas Matthew 7:21 emphasizes that merely calling on the Lord’s name is not enough without doing His will.
Matthew 7:21: Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
Contradiction with Romans 3:20
Zechariah 6:15 speaks of obeying God's commands to be built up, while Romans 3:20 argues that no one is justified by obeying the law.
Romans 3:20: Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law [is] the knowledge of sin.
Contradiction with Galatians 3:10
Zechariah 6:15 implies blessing through obedience, but Galatians 3:10 states those who rely on the law are under a curse.
Galatians 3:10: For as many as are of the works of the law are under the curse: for it is written, Cursed [is] every one that continueth not in all things which are written in the book of the law to do them.
Contradiction with James 2:10
Zechariah 6:15 encourages obedience to commands, whereas James 2:10 declares that breaking one commandment makes one guilty of all.
James 2:10: For whosoever shall keep the whole law, and yet offend in one [point], he is guilty of all.