The great similitude, or rather sameness, both of spirit and expression, which runs through St. John's Gospel and all his epistles, is a clear evidence of their being written by the same person. In this epistle he speaks not to any particular church, but to all the Christians of that age; and in them to the whole Christian church in all succeeding ages. Some have apprehended that it is not easy to discern the scope and method of this epistle. But if we examine it with simplicity, these may readily be discovered. St. John in this letter, or rather tract, (for he was present with part of those to whom he wrote,) has this apparent aim, to confirm the happy and holy communion of the faithful with God and Christ, by describing the marks of that blessed state.

The parts of it are three:

I. The preface,.................................... C. i. 1-4
II. The tract itself,............................ 5-C. v. -12
III. The conclusion,................................... 13-21
In the preface he shows the authority of his own preaching and writing, and expressly points out, verse 3, the design of his present writing. To the preface exactly answers the conclusion, more largely explaining the same design, and recapitulating those marks, by we know thrice repeated, v. 18-20.
The tract itself has two parts, treating,
I. Severally,
1. Of communion with the Father,............... C. i. 5-10
2. Of communion with the Son,................. C. ii. 1-12
With a distinct application to fathers,
young men, and little children,................. 13-27
Whereto is annexed an exhortation to abide in him,......................... 28-C. iii. i-24
That the fruit of his manifestation in the flesh may extend to his manifestation in glory.
3. Of the confirmation and fruit of this abiding through the Spirit,............... C. iv. 1-21
II. Conjointly, Of the testimony of the Father, and Son, and Spirit: on which faith in Christ, the being born of God, love to God and his children, the keeping his commandments and victory over the world, are founded,...... C. v. 1-12
The parts frequently begin and end alike. Sometimes there is an allusion in a preceding part, and a recapitulation in the subsequent. Each part treats of a benefit from God, and the duty of the faithful derived therefrom by the most natural inferences.