I have written unto you, fathers, because ... - The reason assigned here for writing to fathers is the same which is given in the previous verse. It would seem that, in respect to them, the apostle regarded this as a sufficient reason for writing to them, and only meant to enforce it by repeating it. The fact that they had through many years been acquainted with the doctrines and duties of the true religion, seemed to him a sufficient reason for writing to them, and for exhorting them to a steadfast adherence to those principles and duties.
I have written unto you, young men, because ye are strong ... - The two additional circumstances which he here mentions as reasons for writing to young men are, that they are strong, and that the word of God abides in them. The first of these reasons is, that they were strong; that is, that they were qualified for active and useful service in the cause of the Redeemer. Children were yet too young and feeble to appeal to them by this motive, and the powers of the aged were exhausted; but those who were in the vigor of life might be called upon for active service in the cause of the Lord Jesus. The same appeal may be made now to the same class; and the fact that they are thus vigorous is a proper ground of exhortation, for the church needs their active services, and they are bound to devote their powers to the cause of truth. The other additional ground of appeal is, that the word of God abode in them; that is, that those of this class to whom he wrote had showed, perhaps in time of temptation, that they adhered firmly to the principles of religion. They had not flinched from an open defense of the truths of religion when assailed; they had not been seduced by the plausible arts of the advocates of error, but they had had strength to overcome the wicked one. The reason here for appealing to this class is, that in fact they had showed that they could be relied on, and it was proper to depend on them to advocate the great principles of Christianity.