Their ancestors had perished and the former prophets who warned them were no longer alive to continue warning them. They would not have endless opportunities to repent. The punishments that the former prophets had warned the people about had overtaken them. The Lord had pursued and caught the evildoers like a hunter captures his prey. Then they acknowledged that the Lord had indeed done as He had warned them that He would do (cf. Deuteronomy 28:15; Deuteronomy 28:45; 2 Chronicles 36:16). This would be the experience of the contemporary Israelites too if they failed to heed Zechariah"s exhortation (cf. 1 Corinthians 10:11). [source][source][source]
Even though the Israelites had failed God miserably in the past, this introductory message clarified that the Abrahamic Covenant was still in force. God promised to bless His people, but their enjoyment of that blessing in any given generation depended on their walking with Him in trust and obedience. "Repent" (Heb. shub) means "return." It presupposes a previous relationship with God from which His people had departed. [source][source][source]
". . . Zechariah enumerates in his introductory address five great principles: (1) The condition of all God"s blessings, Zechariah 1:3. (2) The evil and peril of disobedience, Zechariah 1:4. (3) The unchangeable character of God"s Word, Zechariah 1:6 a. (4) God"s governmental dealings with His people in accordance with their deeds, Zechariah 1:6 b ("according to our ways and according to our deeds"). (5) God"s immutable purposes, Zechariah 1:6 b ("as Jehovah ... determined ... so did he with us")." [1][source]