What does Revelation 1:4 mean?

From John, to the seven churches in Asia: Grace and peace to you from the One who is, who was, and who is coming, and from the seven spirits before his throne. Revelation 1:4 - Modern Text Bible

(John is writing to seven specific churches, wishing them grace and peace from God (who exists in all times) and from the seven spirits, which represent God’s fullness.)