Albert Barnes Commentary 1 John 5:13

"These things have I written unto you, that ye may know that ye have eternal life, [even] unto you that believe on the name of the Son of God." — 1 John 5:13 (ASV)

These things have I written unto you. This refers to the things in this epistle concerning the testimony borne to the Lord Jesus.

That believe on the name of the Son of God. To believe on his name is to believe on himself—the word name often being used to denote the person (Matthew 28:19).

That ye may know that ye have eternal life. That you may see the evidence that eternal life has been provided, and that you may be able, by self-examination, to determine whether you possess it (John 20:31).

And that ye may believe, etc. That is, that you may continue to believe, or may persevere in believing. He was assured that they actually did believe on him then, but he was eager to set before them the nature of religion in such a way that they would continue to exercise faith in him.

It is often one of the most important duties of ministers of the gospel to present to real Christians such views of the nature, the claims, the evidences, and the hopes of religion as are adapted to secure their perseverance in the faith.

In the human heart, even when converted, there is such a proneness to unbelief. The religious affections so easily become cold. There are so many cares pertaining to the world that are suited to distract the mind, and so many allurements of sin to draw the affections away from the Saviour. For these reasons, there is a need to be constantly reminded of the nature of religion, so that the heart may not be wholly estranged from the Saviour.

No small part of preaching, therefore, must consist of the restatement of arguments by which the mind has previously been fully convinced; of motives whose force has once been felt and acknowledged; and of the grounds of hope, peace, and joy which have already, on previous occasions, diffused comfort through the soul.

It is no less important to keep the soul than it is to convert it; to save it from coldness, deadness, and formality than it was to impart to it the elements of spiritual life at first. It may be as important to trim a vine, if one wishes to have grapes, as it is to set it out; to keep a garden from being overrun with weeds in the summer, as it was to plant it in the spring.