1 Kings 1:32

We have here the effectual care David took both to secure Solomon's right and to preserve the public peace, by crushing Adonijah's project in the bud. Observe, I. The express orders he gave for the proclaiming of Solomon. The persons he entrusted with this great affair were Zadok, Nathan, and Benaiah, men of power and interest whom David had always reposed a confidence in and found faithful to him, and whom Adonijah had passed by in his invitation, Kg1 1:10. David orders them forthwith, with all possible solemnity, to proclaim Solomon. They must take with them the servants of their lord, the lifeguards, and all the servants of the household. They must set Solomon on the mule the king used to ride, for he kept not such stables of horses as his son afterwards did. He appoints them whither to go (Kg1 1:33 and Kg1 1:34, Kg1 1:35), and what to do. 1. Zadok and Nathan, the two ecclesiastical persons, must, in God's name, anoint him king; for though he was not the first of his family, as Saul and David were, yet he was a younger son, was made king by divine appointment, and his title was contested, which made it necessary that hereby it should be settled. This unction was typical of the designation and qualification of the Messiah, or Christ, the anointed one, on whom the Spirit, that oil of gladness, was poured without measure, Heb 1:9, Psa 89:20.

— Matthew Henry's Concise Commentary (public domain)