The Greek word γράφω to write is used 29 times in Revelation. It is a running theme in this book.
which said: "Write on a scroll what you see and send it to the seven churches: to Ephesus, Smyrna, Pergamum, Thyatira, Sardis, Philadelphia and Laodicea."
John is periodically reminded to record what he sees and hears throughout the whole book. Just before the verse that you quoted, we have
Then the angel said to me, "Write this: Blessed are those who are invited to the wedding supper of the Lamb!" And he added, "These are the true words of God."
Then John continues to see and hear more things till
He who was seated on the throne said, "I am making everything new!" Then he said, "Write this down, for these words are trustworthy and true."
In its immediate context, "these words" refers to what he has heard since after Revelation 19:9.
Another theme of this book is the emphasis on the truthfulness of the words he hears. As John continues in
The angel said to me, "These words are trustworthy and true. The Lord, the God who inspires the prophets, sent his angel to show his servants the things that must soon take place."
Jesus said to them, "Very truly I tell you, it is not Moses who has given you the bread from heaven, but it is my Father who gives you the true bread from heaven.
In Revelation, John receives true words from the glorious heavenly Jesus.
And if anyone takes words away from this scroll of prophecy, God will take away from that person any share in the tree of life and in the Holy City, which are described in this scroll.
Bread sustains our physical life. Indeed, John's recorded words in Revelation sustains our eternal life.