Now in the eighteenth year of king Jeroboam the son of Nebat reigned Abijam over Judah.

Now in the eighteenth year of the reign of Jeroboam the son of Nabat, Abiam reigned over Juda.

Now in the eighteenth year of king Jeroboam, the son of Nebat, Abijam became king over Judah.

Then, in the eighteenth year of the reign of Jeroboam, the son of Nebat, Abijam reigned over Judah.

Reigned Abijam over Judah - Of this son of Rehoboam, of his brethren, and of Rehoboam's family in general, see 2-Chronicles 12, where many particulars are added.

Now in the eighteenth year of King Jeroboam the son of Nebat reigned Abijam over Judah. That is, began to reign; and by this it appears that Rehoboam was in the eighteenth year of his reign when he died, for he and Jeroboam began their reign at the same time.

Abijam's heart was not perfect with the Lord his God; he wanted sincerity; he began well, but he fell off, and walked in all the sins of his father, following his bad example, though he had seen the bad consequences of it. David's family was continued as a lamp in Jerusalem, to maintain the true worship of God there, when the light of Divine truth was extinguished in all other places. The Lord has still taken care of his cause, while those who ought to have been serviceable thereto have lived and perished in their sins. The Son of David will still continue a light to his church, to establish it in truth and righteousness to the end of time. There are two kinds of fulfilling the law, one legal, the other by the gospel. Legal is, when men do all things required in the law, and that by themselves. None ever thus fulfilled the law but Christ, and Adam before his fall. The gospel manner of fulfilling the law is, to believe in Christ who fulfilled the law for us, and to endeavour in the whole man to obey God in all his precepts. And this is accepted of God, as to all those that are in Christ. Thus David and others are said to fulfil the law.

ABIJAM'S WICKED REIGN OVER JUDAH. (1-Kings 15:1-8)
Abijam--His name was at first Abijah (2-Chronicles 12:16); "Jah," the name of God, according to an ancient fashion, being conjoined with it. But afterwards, when he was found "walking in all the sins of his father" [1-Kings 15:3], that honorable addition was withdrawn, and his name in sacred history changed into Abijam [LIGHTFOOT].

Reign of Abijam (cf., 2 Chron 13). - Abijam reigned three years, and his mother's name was Maacah, daughter (i.e., grand-daughter) of Absalom. We have the same in 2-Chronicles 11:20-21; but in 2-Chronicles 13:2 she is called Michajahu, daughter of Uriel of Gibeah. If אבישׁלום was without doubt Absalom, the well-known son of David, as we may infer from the fact that this name does not occur again in the Old Testament in connection with any other person, since Absalom had only one daughter, viz., Thamar (2-Samuel 14:27), who was fifty years old when Solomon died, Maacah must have been a daughter of this Thamar, who had married Uriel of Gibeah, and therefore a grand-daughter of Absalom. This is sustained by Josephus (Ant. viii. 10, 1). The form of the name מיכיהוּ is probably an error in copying for מעכה, as the name is also written in 2-Chronicles 11:20, 2-Chronicles 11:21, and not a different name, which Maacah assumed as queen, as Caspari supposes (Micha, p. 3, note 4).

Abijam reigned - So his reign began with Jeroboam's eighteenth year, continued his whole nineteenth year, and ended within his twentieth year, in which also Asa's reign began. And thus one and the same year may be attributed to two several persons.