The Apostle Paul
Colossians 1:26BSB·traditional attribution

the mystery that was hidden for ages and generations but is now revealed to His saints.

John Calvin Reformed @genevareformer

26. Hidden mystery. Here we have a commendation of the gospel — that it is a wonderful secret of God. It is not without good reason that Paul so frequently extols the gospel by bestowing upon it the highest commendations in his power; for he saw that it was a stumblingblock to the Jews, and foolishness to the Greeks.

Matthew Henry Presbyterian @wholebiblehenry

Here is a summary of the doctrine of the gospel concerning the great work of our redemption by Christ. It comes in here not as the matter of a sermon, but as the matter of a thanksgiving; for our salvation by Christ furnishes us with abundant matter of thanksgiving in every view of it: Giving thanks unto the Father, Col 1:12.

Commenting on Colossians 1:12-29

John Gill Reformed Baptist @doctorgill

Even the mystery which hath been hid from ages and generations,.... This is said, as explanative of the word of God; signifying that he did not mean the Scriptures in general, which are the word of God, and every part of them; some part of which is historical, another prophetical, another practical, and another doctrinal; nor the law, which also is the word of God...