Back in Revelation 1:11 John had received the instruction to “write what you see in a book and send it to the seven churches.” John had studiously obeyed that instruction, diligently recording all the details contained thus far in the book of Revelation. In that sense John did not need to be told again to “write.” But (as in Revelation 14:13) John now receives a special word to which he must give extra care that it is written down. In other words, with the (repeated) command to “write,” John (and the churches who read this) learn that the statement John is explicitly told to write down is vitally important.
9 And the angel said to me, “Write this: Blessed are those who are invited to the marriage supper of the Lamb.” And he said to me, “These are the true words of God.”