John Chrysostom
This too is something new and unusual. We nowhere encounter the word "amen" at the beginning and in the preface of the epistles. Usually it is placed after many discussions.
Here, however, wishing to show that what had been said contains sufficient reproof of the Galatians, and that his speech is completely finished, he placed this word at the beginning of the epistle.
Obvious transgressions do not require lengthy preparations for their reproof.
Therefore, after mentioning the cross and resurrection, the redemption of sins, security from them for the future, the will of the Father and the agreement of the Son, grace, peace, and every gift of God, he concluded his speech with doxology.
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He did this not only for that reason, but also from excessive wonder before the greatness of the gift and the abundance of grace.
He considered what we were, and what God made us beyond our expectation and in the shortest time.
Being unable to express this in words, he concluded his speech with doxology, sending up praise to God on behalf of the whole world.
It was not praise worthy of Him, but such as was possible for him.
This is why, after this, he continues his speech with still greater force, inflamed as if by a mighty flame from the contemplation of God's benefactions.