Contradiction with Matthew 10:14
Zechariah 8:20 speaks of people seeking the Lord and going to pray, whereas Matthew 10:14 describes those who reject the message and are not receptive.
Matthew 10:14: And whosoever shall not receive you, nor hear your words, when ye depart out of that house or city, shake off the dust of your feet.
Contradiction with Jeremiah 7:16
Zechariah 8:20 envisions people from many cities seeking God, while Jeremiah 7:16 instructs not to pray for certain people due to their disobedience and rejection of God.
Jeremiah 7:16: Therefore pray not thou for this people, neither lift up cry nor prayer for them, neither make intercession to me: for I will not hear thee.
Contradiction with 2 Kings 17:15
Zechariah 8:20 talks about people desiring to worship God, whereas 2 Kings 17:15 describes people who rejected God and His statutes.
2 Kings 17:15: And they rejected his statutes, and his covenant that he made with their fathers, and his testimonies which he testified against them; and they followed vanity, and became vain, and went after the heathen that [were] round about them, [concerning] whom the LORD had charged them, that they should not do like them.
Contradiction with Amos 5:21-23
Zechariah 8:20 promotes people going to seek God, but Amos 5:21-23 expresses God's rejection of certain worship practices despite people's efforts to seek Him.
Amos 5:21-23: I hate, I despise your feast days, and I will not smell in your solemn assemblies. [in...: or, your holy days]
Contradiction with Malachi 1:10
Zechariah 8:20 encourages prayer and worship, while Malachi 1:10 criticizes insincere worship and suggests God does not delight in all offerings.
Malachi 1:10: Who [is there] even among you that would shut the doors [for nought]? neither do ye kindle [fire] on mine altar for nought. I have no pleasure in you, saith the LORD of hosts, neither will I accept an offering at your hand.
Contradiction with Isaiah 1:15
Zechariah 8:20 suggests that God will be sought and people will pray, whereas Isaiah 1:15 indicates that God will hide His eyes and not listen to prayers due to iniquity.
Isaiah 1:15: And when ye spread forth your hands, I will hide mine eyes from you: yea, when ye make many prayers, I will not hear: your hands are full of blood. [make...: Heb. multiply prayer] [blood: Heb. bloods]