Albert Barnes on Revelation 7:12

Saying, Amen. Rev 1:7. The word Amen here is a word strongly affirming the truth of what is said, or expressing hearty assent to it. It may be uttered, as expressing this, either in the beginning or end of a sentence. Thus wills are commonly commenced, "In the name of God, Amen."

Blessings and glory, etc. Substantially the same ascription of praise occurs in Rev 5:12. Rev 5:12. The general idea is, that the highest kind of praise is to be ascribed to God; everything excellent in character is to be attributed to him; every blessing which is received is to be traced to him. The order of the words indeed is changed, but the sense is substantially the same. In the former case (Rev 5:12) the ascription of praise is to the Lamb-- the Son of God; here it is to God. In both instances the worship is described as rendered in heaven; and the use of the language shows that God and the Lamb are regarded in heaven as entitled to equal praise. The only words found here which do not occur in Rev 5:12 are thanksgiving and might--words which require no particular explanation.

(a) "saying" Rev 5:13,14