After John saw (and heard) the first angel flying in mid-heaven, he spotted a second angel following behind the first (hence also flying in mid-heaven). This angel, too, had obviously received a commission from God to carry out a specific task (see Psalm 103:20–21; Hebrews 1:14). The eternal gospel embodied in the triple commands of the first angel need follow up in order to give earthlings more reason to fear God, give him glory and worship him. The implication is that humanity refuses to take the instruction of the first angel to heart.
8 Another angel, a second, followed, saying, “Fallen, fallen is Babylon the great, she who made all nations drink the wine of the passion of her sexual immorality.”