This refers to the sequence in which chs. 17 and 18 were revealed to John, not necessarily to the sequence of events therein recorded. John does not mean that the events of ch. 18 take place subsequently to all of those referred to in ch. 17. See on ch. 4:1.
Another angel.
That is, another than the angel of ch. 17. This angel unites with the third angel of ch. 14:9-11 in the proclamation of God’s final message to the world (EW 277), and his message is a repetition of that of the second angel of ch. 14:8 (GC 603).
From heaven.
The angel is represented as having come forth from the presence of God on a special mission, and in the act of descending to earth, at the time John saw him.
Power.
Gr. exousia, “authority” (see on ch. 17:13). This angel comes forth from the throne room of the universe; commissioned to proclaim God’s last message of mercy and to warn the inhabitants of earth of the imminent fate awaiting “Babylon the great.”
Lightened.
Or, “illuminated.” Despite satanic efforts to shroud the earth in darkness, God now sets it ablaze with the glorious light of saving truth (see on John 1:4, 5, 9).
Glory.
Gr. doxa (see on John 1:14; Rom. 3:23). The “glory” may be thought of as representing the character of God (cf. Ex. 33:18, 19; 34:6, 7), here particularly as revealed in the plan of salvation.