A loud voice from the temple: the voice comes from the temple, or sanctuary, in heaven. Since 15.8 says that there was no one in the temple now, this command comes from God (10.4). See 14.15 on other ways to translate loud voice.

Go and pour: the angels are in heaven (15.1), and they must go out in order to pour out on the earth the contents of their bowls. So Go is the right verb to use in this context.

Pour out … the seven bowls: this can be stated “empty out … the seven bowls.” In some languages it may be necessary to specify what is to be poured out; if so, something like the following can be said: “Go and pour out on the earth the wine of God’s anger that is in the (seven) bowls” (see 14.10).

Quoted with permission from Bratcher, Robert G. and Hatton, Howard A. A Handbook on The Revelation to John. (UBS Handbook Series). New York: UBS, 1993. For this and other handbooks for translators see here .