“secret messengers.” The Hebrew word is ragal (#07270 רָגַל), a word which describes a lot. It can mean to go on foot or walk about on foot; to be a slanderer or gossip; to go as a spy or scout. This range of meanings is the reason for the many different translations in the English versions: BBE (watchers); CJB, JPS, KJV, NASB (spies); HCSB (messengers); ESV, NIV, NLT, RSV (secret messengers); NJB (couriers); TNK (agents); Schocken Bible (spy-runners).
Given the fact that these agents of Absalom were not “spies” in the traditional sense but were actually his agents that in this context were to deliver a message to Absalom’s contacts around Israel, “secret messengers” seemed to be a good translation, although the Tanakh’s translation “agents” is also very good.
“shofar.” The ram’s horn trumpet, not the metal trumpet. The shofar can be heard for a mile or more, but for the sound to cover all Israel, Absalom would have had to have had a network of shofar blowers.
“Absalom reigns as king in Hebron.” One thing that is conspicuously missing from Absalom’s claim to the throne is that David’s second son, Chileab (2 Sam. 3:3 but called “Daniel” in 1 Chron. 3:1), would have the claim to the throne over Absalom. This is quite certain evidence that Chileab had died since he is not mentioned in any of the records. In fact, Chileab likely died very young since nothing is ever said about him other than he was David’s second son (2 Sam. 3:3).
Absalom was killed in battle and never got to become king. However, his grandson Abijah did become king of Judah. Absalom’s wife gave birth to Maacah, who married Rehoboam the son of Solomon, and then the son of Maacah and Rehoboam was Abijah, who became the king of Judah (2 Chron. 11:20; 1 Kings 11:43; 14:31-15:1).