John Gill emphasizes the assurance of eternal life for believers in his sermon on 1 John 5:13. He explains that the apostle John wrote to affirm the victory over the world through faith in Christ, who is the Son of God. The purpose of this writing is to instill confidence in believers about their eternal life, which is a gift from God, and to encourage them to continue in their faith. Gill highlights the importance of knowing and believing in the name of the Son of God for righteousness, life, and salvation. He concludes that the sacred writings serve to strengthen and increase faith in Christ.

Ver. 13. These things have I written unto you,.... Which are contained in the epistle in general, and particularly what is written in the context, concerning the victory of the world, being ascribed to him who believes that Christ is the Son of God; and concerning the six witnesses of his sonship, and the record bore by God, that the gift of eternal life is in him: and which are especially written to them, that believe on the name of the Son of God; who not only believed that Christ is the Son of God, which this six fold testimony would confirm them in, but also believed in his name for righteousness, life, and salvation; in which name there is all this, and in no other; and who also professed their faith in him, and were baptized in his name, and continued believing in him, and holding fast their profession of him. The end of writing these things to them was, that ye may know that ye have eternal life; that there is such a thing as eternal life; that this is in Christ; that believers have it in him, and the beginning of it in themselves; and that they have a right unto it, and meetness for it, and shall certainly enjoy it; the knowledge of which is had by faith, under the testimony of the Spirit of God, and particularly what is above written concerning eternal life, being a free grace gift of God; and this being in Christ, and the assurance of it, that such who have him, or believe in him, have that which might serve to communicate, cultivate, and increase such knowledge: and that ye may believe on the name of the Son of God; which they had done already, and still did; the sense is, the above things were written to them concerning the Son of God, that they might be encouraged to continue believing in him, as such; to hold fast the faith of him and go on believing in him to the end; and that their faith in him might be increased; for faith is imperfect and is capable of increasing, and growing exceedingly: and nothing more tends unto, or is a more proper means of it, than the sacred writings, the reading and hearing them explained, and especially that part of them which respects the person, office, and grace of Christ. The Alexandrian copy, and one of Beza's manuscripts, the Vulgate Latin, Syriac, and Ethiopic versions, read, "these things have I written unto you, that ye may know that ye have eternal life, who believe in the name of the Son of God".