Zechariah is the book that is taken on today.
For Zechariah we can nail down a more precise date than the previous MPs we have studied so far - 1:1 places his career starting around BC 520. Zechariah receives his prophesy via vision (actually, many visions). By the time of Zechariah's ministry, it had been about 20 since their return from exile in Babylon (BC 538). Though Israel had laid the foundation of the temple shortly after their return in BC 538, the oppressive taxes and many other factors, including Israel's continued moral slide, allowed Israel to conclude the Lord was not with them, and building the temple became nearly impossible. Zechariah is speaking to a discouraged people who are not seeing what the prophets of the exile had promised would happen, namely a restored and rebuilt Jerusalem. Thus, faithful obedience of the people of God was viewed as worthless, and the temptation was to pursue any path, even outside the Lord's covenant, that would provide success and happiness.
1) The Messiah: The Messianic predictions in Zechariah remind Israel that the Lord has not forgotten them nor His promise to the line of David from 2 Samuel 7. In Zechariah's prophesy, no earthly ruler is mentioned, only the Messiah. In this Davidic Messiah, both priestly and royal functions are combined. He is refered to as "the branch" (3:8; 6:12), "the one they pierced" (12:10), and "the Shepherd" (13:7ff). These Messianic prophesies are why Zechariah is so often quoted in the NT (9.9 in Mt. 21.5, Jn. 12.15; 11.13 in Mt. 27.9; 12.10 in Jn. 19.37; 13.7 in Mt. 26.31, Mk. 14.27) - other themes in 3.2 in Jude 9.23 and 8.16 in Eph. 4.25. He is the one who "shall branch out from his place and he shall build the temple of the Lord... and shall bear royal honor... and the crown shall be in the temple of the Lord as a reminder" (6.12-14).
2) Covenant faithfulness: The Lord has not forgotten His promises to His people. He will restore His people, and be faithful to them, though at the time of Zechariah this appears not to be the case.
The Lord is patient with His people, and even after exile - where the Lord clearly demonstrated His sovereignty over nations and history, Israel's still considers in their despair to pursue other gods in their pragmatism. But the Lord is clear. A Messiah is coming, and not just any Messiah. This Messiah will be a ruler and a priest, and will be in the line of David, as God had promised long before. The Lord is with His people. He has not forgotten His mission to establish His Kingdom on earth and redeem all things to Himself via "the one who is pierced".
"And in this day there shall be inscribed on the bells of the horses, "Holy to the Lord." Zech. 14:20