The Apostle Paul
Romans 14:6ESV·traditional attribution

The one who observes the day, observes it in honor of the Lord. The one who eats, eats in honor of the Lord, since he gives thanks to God, while the one who abstains, abstains in honor of the Lord and gives thanks to God.

John Calvin Reformed @genevareformer

6. He who regards a day, etc. Since Paul well knew that a respect for days proceeded from ignorance of Christ, it is not probable that such a corruption was altogether defended by him; and yet his words seem to imply, that he who regarded days committed no sin; for nothing but good can be accepted by God.

Matthew Henry Presbyterian @wholebiblehenry

We have in this chapter, I. An account of the unhappy contention which had broken out in the Christian church. Our Master had foretold that offences would come; and, it seems, so they did, for want of that wisdom and love which would have prevented discord, and kept up union among them. 1.

Commenting on Romans 14:1-23

John Gill Reformed Baptist @doctorgill

He that regardeth the day, regardeth it to the Lord,.... The apostle strengthens the above advice with this reason, because what is done both by one and the other, is done unto the Lord. The weak brother that esteems one day above another, and regards the passover, pentecost, and feast of tabernacles, a new moon, or a seventh day sabbath, does it in obedience to...