The Apostle Paul
Ephesians 1:9BSB·traditional attribution

And He has made known to us the mystery of His will according to His good pleasure, which He purposed in Christ

John Calvin Reformed @genevareformer

9. Having made known to us the mystery of his will. Some were alarmed at the novelty of his doctrine. With a view to such persons, he very properly denominates it a mystery of the divine will, and yet a mystery which God has now been pleased to reveal. As he formerly ascribed their election, so he now ascribes their calling, to the good pleasure of God.

Matthew Henry Presbyterian @wholebiblehenry

He begins with thanksgivings and praise, and enlarges with a great deal of fluency and copiousness of affection upon the exceedingly great and precious benefits which we enjoy by Jesus Christ. For the great privileges of our religion are very aptly recounted and enlarged upon in our praises to God. I.

Commenting on Ephesians 1:3-14

John Gill Reformed Baptist @doctorgill

Having made known unto us the mystery of his will,.... The Gospel, which is a mystery, a hidden mystery, the mystery of God and of Christ, and the mystery of the Gospel; the several doctrines of it are called the mysteries of the kingdom of heaven; such as are concerning the trinity of persons in the Godhead, the union of the two natures in Christ...