Albert Barnes Commentary Exodus 19:5

"Now therefore, if ye will obey my voice indeed, and keep my covenant, then ye shall be mine own possession from among all peoples: for all the earth is mine:" — Exodus 19:5 (ASV)

A peculiar treasure - A costly possession acquired with exertion and carefully guarded. The special relation in which Israel stands, taken out of the pagan world and consecrated to God as His slaves, subjects, and children, determines their privileges and is the foundation of their duties. The same principle applies even in a stronger sense to the Church. See (Acts 20:28; 1 Corinthians 6:20; 1 Peter 2:9).

All the earth is mine - It was a point of great practical importance, to impress upon the Jews that their God was no mere national Deity. Compare (Deuteronomy 10:14; Psalms 24:1).