Many commentators believe that Solomon ruled Israel alongside David for a handful of years before David died. This followed ancient Near Eastern custom, and co-regency certainly would have afforded Solomon time to learn the ways of a king. But once David died, Solomon alone was king, and he set about dealing with the threats to his kingdom.
The first threat to be addressed was Solomon’s older brother Adonijah. Remember that Adonijah, seeing David’s deteriorating health, attempted to gather the support of Israel’s leaders and succeed his father as king. Swift, wise action by Nathan the prophet and Solomon’s mother Bathsheba prevented Adonijah’s ascension, and Solomon promised to spare his brother’s life as long as he behaved himself (1 Kings 1). Eventually, however, Adonijah showed his true colors as one who still coveted David’s throne.
We see his desire for David’s throne first in his statement to Bathsheba that “you know that the kingdom was mine, and that all Israel fully expected me to reign” (2:15). Adonijah overstated things, for his attempt to secure Israel’s support did not get very far before Solomon was anointed king (1:5–53). But the fact that he could say such a thing meant that he still had designs on the kingdom. Moreover, Adonijah’s request for David’s concubine Abishag as a wife removed any doubts about his intentions (2:16–18). For a son to take his father’s concubine as his wife violated the spirit of the law (Deut. 22:30; see Gen. 35:22; 49:3–4), but perhaps more significant for understanding today’s passage, to take one of a ruler’s concubines in the ancient Near East was to make a claim on the throne of a nation (see 2 Sam. 16:20–23). Solomon saw right through this plot and had Adonijah executed. As long as Adonijah lived, he was a threat to the kingdom, so Solomon removed him (1 Kings 2:19–25).
As we saw in 1 Kings 1:7, Abiathar the priest supported Adonijah to succeed David. Dispatching Adonijah gave Solomon the opportunity to remove his rival’s supporters as well. However, Solomon did not have Abiathar killed because he had been loyal to David and, presumably, was not a continuing threat to Solomon’s rule. Solomon merely deposed him from the priesthood (2:26–27). Abiathar was a descendant of the priest Eli, so his deposition finally fulfilled God’s pledge to remove Eli’s family from the priesthood, a promise made decades earlier (1 Sam. 2:27–36; 14:3; 22:20).