It was common in the ancient Near East for the author to speak and someone else to write down the words. Many of the New Testament letters were written this way. Paul wrote the final greeting himself.
Paul refers to a "secret truth" in this chapter. The role of the church in the plans of God was once unknown. But God has now revealed it. Part of this involves the Gentiles having equal standing with the Jews in the plans of God. (See: [[rc://en/tw/dict/bible/kt/reveal]])