John Gill Commentary Romans 1:25

"for that they exchanged the truth of God for a lie, and worshipped and served the creature rather than the Creator, who is blessed for ever. Amen." — Romans 1:25 (ASV)

Who changed the truth of God into a lie
Not the truth of the Gospel, which they were unacquainted with; but that which might be known of God as true, and was known of them by the light of nature; or the true God himself, whom they "changed into a lie"; by ascribing to false deities, which were lying vanities, those things which were known of God; and by worshipping them instead of him: for they

worshipped and served the creature more than the Creator ;
or "above him" or "against him", in opposition to him, or "besides him", others along with him; or neglecting him, and not worshipping him at all; which is aggravated in that what they worshipped was a creature, either of their own, or of God's making, and whom they neglected was the Creator of them:

who is blessed for ever, Amen ;
is blessed in himself, and the fountain of all blessedness to his creatures; which is so glaring a truth, that everyone ought to say and set his "Amen" to it.