John Calvin Commentary Romans 14:10

"But thou, why dost thou judge thy brother? or thou again, why dost thou set at nought thy brother? for we shall all stand before the judgment-seat of God." — Romans 14:10 (ASV)

But you, why do you, etc. As he had made the life and death of us all subject to Christ, he now proceeds to mention the authority to judge, which the Father has conferred on him, together with the dominion over heaven and earth. From this, he concludes that it is an unreasonable boldness in anyone to assume the power to judge his brother, since by taking such a liberty he robs Christ the Lord of the power which he alone has received from the Father.

But first, by the term brother, he checks this lust for judging; for since the Lord has established among us the right of a fraternal alliance, an equality ought to be preserved. Everyone, therefore, who assumes the character of a judge acts unreasonably.

Secondly, he calls us before the only true judge, from whom no one can take away his power, and whose tribunal no one can escape. So then, just as it would be absurd among men for a criminal, who ought to occupy a humble place in the court, to ascend the tribunal of the judge, so it is absurd for a Christian to take to himself the liberty of judging the conscience of his brother.

A similar argument is mentioned by James, when he says that he who judges his brother, judges the law, and that he who judges the law, is not an observer of the law but a president; and, on the other hand, he says that there is but one lawgiver, who can save and destroy (James 4:12).

He has ascribed tribunal to Christ, which means his power to judge, just as the voice of the archangel, by which we shall be summoned, is called a trumpet in another place; for it will pierce, as it were, with its sound, into the minds and ears of all.