Calvin's Commentaries, Vol. 45: Catholic Epistles, tr. by John King, [1847-50], at sacred-texts.com
It appears from the writings of Jerome and Eusebius, that this Epistle was not formerly received by many Churches without opposition. There are also at this day some who do not think it entitled to authority. I, however, am inclined to receive it without controversy, because I see no just cause for rejecting it. For what seems in the second chapter to be inconsistent with the doctrine of free justification, we shall easily explain in its own place. Though he seems more sparing in proclaiming the grace of Christ than it behooved an Apostle to be, it is not surely required of all to handle the same arguments. The writings of Solomon differ much from those of David; while the former was intent on forming the outward man and teaching the precepts of civil life, the latter spoke continually of the spiritual worship of God, peace of conscience, God’s mercy and gratuitous promise of salvation. But this diversity should not make us to approve of one, and to condemn the other. Besides, among the evangelists themselves there is so much difference in setting forth the power of Christ, that the other three, compared with John, have hardly sparks of that full brightness which appears so conspicuous in him, and yet we commend them all alike.
It is enough to make men to receive this Epistle, that it contains nothing unworthy of an Apostle of Christ. It is indeed full of instruction on various subjects, the benefit of which extends to every part of the Christian life; for there are here remarkable passages on patience, prayer to God, the excellency and fruit of heavenly truth, humility, holy duties, the restraining of the tongue, the cultivation of peace, the repressing of lusts, the contempt of the world, and the like things, which we shall separately discuss in their own places.
But as to the author, there is somewhat more reason for doubting. It is indeed certain that he was not the Son of Zebedee, for Herod killed him shortly after our Lord’s resurrection. The ancients are nearly unanimous in thinking that he was one of the disciples named Oblias and a relative of Christ, who was set over the Church at Jerusalem; and they supposed him to have been the person whom Paul mentioned with Peter and John, who he says were deemed pillars, (Ga 2:9.) But that one of the disciples was mentioned as one of the three pillars, and thus exalted above the other Apostles, does not seem to me probable. I am therefore rather inclined to the conjecture, that he of whom Paul speaks was the son of Alpheus. I do not yet deny that another was the ruler of the Church at Jerusalem, and one indeed from the college of the disciples; for the Apostles were not tied to any particular place. But whether of the two was the writer of this Epistle, it is not for me to say. That Oblias was actually a man of great authority among the Jews, appears even from this, that as he had been cruelly put to death by the faction of an ungodly chief-priest, Josephus hesitated not to impute the destruction of the city in part to his death.