Jamieson, Fausset and Brown on Revelation 5:14

14. said--So A, Vulgate, and Syriac read. But B and Coptic read, "(I heard) saying."

Amen--So A reads. But B reads, "the (accustomed) Amen." As in Re 4:11, the four and twenty elders asserted God's worthiness to receive the glory, as having created all things, so here the four living creatures ratify by their "Amen" the whole creation's ascription of the glory to Him.

four and twenty--omitted in the oldest manuscripts: Vulgate supports it.

him that liveth for ever and ever--omitted in all the manuscripts: inserted by commentators from Re 4:9. But there, where the thanksgiving is expressed, the words are appropriate; but here less so, as their worship is that of silent prostration. "Worshipped" (namely, God and the Lamb). So in Re 11:1, "worship" is used absolutely.