Jotham took the throne when his father, Uzziah (Azariah), died. He reigned sixteen years, and did what was right in the sight of the Lord. He built the Upper Gate of the house of the Lord. During his reign, Rezin of Syria and Pekah of Israel came against Judah. Jotham died, and Ahaz–his son–reigned in his place.
Ahaz reigned sixteen years in Jerusalem, and he did not do what was right in the eyes of the Lord. He adopted many of the practices of the kings of Israel, passing his son through the fire (presumably to Molech), burning incense on the high places. Rezin and Pekah fought against Ahaz, but could only take one territory, Elath, which the Edomites inhabited. Ahaz sent word to Tiglath-Pileser of Assyria, asking for his military assistance, and sent him the silver and gold which was in the treasuries of the king’s house. Assyria agreed, and attached Damascus, killing Rezin. Ahaz went to Damascus to observe what was happening. While there, he saw an altar, and sent a description to Urijah the priest to build one in Jerusalem. When Ahaz returned, he offered sacrifices on the new altar. From that point on, he ordered that all sacrifices be offered on the new altar, and the old bronze altar would be used by the king to inquire (or seek a divine word). Ahaz cut the panels off the carts and removed the lavers, took down the Sea from the bronze oxen, and set it on pavement. He removed the Sabbath pavilion from the temple, and the king’s entrance from the house of the Lord, all on account of the king of Assyria.
The main lesson here is the acquisition of allies. Much like Menahem gave Pul of Assyria a large sum of money not to attack Israel, now Ahaz gave a large sum to Tiglath-Pileser to protect Judah from Syria. So Ahaz made several unholy alliances: one with Tiglath-Pileser of Assyria, an idolatrous and ungodly king who began to control not only his actions, but also his worship style, one with Israel (his enemy at the time) of a spiritual nature in that he began to worship idols like Israel did, and one with Rezin of Syria in that he copied his altar and began to offer sacrifices to Yahweh on this foreign idolatrous altar. When you begin to ally yourself with ungodly and idolatrous people, the effect it has on you is certain: you will begin to adopt their ways and pull away from God. Re-evaluate your alliances, your friendships, your business associations. Be aware of who it is with whom you align your path. Make sure that you are walking on the same Godly path. If not, you may be diverted onto a path that will lead to destruction, just as it did for Israel and Judah.