Albert Barnes Commentary Exodus 19:6

"and ye shall be unto me a kingdom of priests, and a holy nation. These are the words which thou shalt speak unto the children of Israel." — Exodus 19:6 (ASV)

A kingdom of priests - Israel collectively is a royal and priestly race: a dynasty of priests, each true member uniting in himself the attributes of a king and priest. Compare 1 Peter 2:5; Revelation 1:6.

An holy nation - The holiness of Israel consisted in its special consecration to God: it was a sacred nation, sacred by adoption, by covenant, and by participation in all means of grace. Compare Deuteronomy 7:6; Deuteronomy 26:19; Deuteronomy 28:9; 1 Corinthians 3:17; 1 Thessalonians 5:27.