me ... live - by coming to me ye shall live: for “I am the life” (Joh 14:6).
everlasting covenant - (Jer 32:40; 2Sa 23:5).
with you ... David - God’s covenant is with the antitypical David, Messiah (Eze 34:23), and so with us by our identification with Him.
sure - answering to “everlasting,” irrevocable, unfailing, to be relied on (Psa 89:2-4, Psa 89:28, Psa 89:29, Psa 89:34-36; Jer 33:20, Jer 33:21; 2Sa 7:15, 2Sa 7:16; 2Co 1:18-20).
mercies of David - the mercies of grace (Isa 63:7; Joh 1:16) which I covenanted to give to David, and especially to Messiah, his antitype. Quoted in Act 13:34.