I write this to you is a phrase that is repeatedly used in this Letter to introduce a warning (as in 2.1 and 26) or to emphasize an assurance (as in 2.12-14, 21). The latter is the case also in the present verse. For “to write” see comments on 1.4; for the use of the aorist tense, see the note on “I am writing” in 2.12.

The demonstrative pronoun this points back. Its reference is not to a specific passage but to all which precedes in this Letter, in which the readers have been assured again and again that their salvation is certain; see for example 1.3; 2.12-14; 3.1, 14; 4.13. To bring this out one may say ‘all this I write to you.’

The order in which Revised Standard Version gives the next two clauses is the reversal of what the Greek has. The following discussion will keep to the Greek clause order.

That you may know that you have eternal life: the clause follows in the Greek directly after “I write this to you.” It says what is the aim of the assurances that have been given in this Letter. Accordingly the first that has the force of “in order that.” You have is in the present tense, indicating that to have eternal life is not a future but a present reality.

“To know” is often rendered ‘to be sure,’ ‘to be assured,’ ‘to have no doubt.’ Similarly in verse 15, where the verb occurs twice in this sense.

You have eternal life: in the Greek the adjective is separated from its noun by the verb and so is emphatic by position. To bring this out one may say ‘you have life that is eternal,’ ‘you have life—yes, eternal life.’ If one has to restructure the clause, one may say ‘eternal/true life is dwelling in you,’ ‘you are living for the age to come.’ Compare also comments on 3.15, and on “to have life” in 5.12.

You who believe in the name of the Son of God: this clause is an appositional clause going with “to you” in the main clause. In the Greek the two are separated by the “that” clause. This syntactically unusual position serves to lend the clause special emphasis. To bring this out one may use a rendering of the sentence such as “I write you this so that you may know that you have eternal life—you that believe in…” (Good News Translation). In some cases the clause requires a rendering by a full sentence such as ‘I write this to you that you may know … eternal life. I am addressing you (or I mean you) who believe in…’; in other cases it may have to be transposed, ‘you who believe in…, I write these things to you that you may know … eternal life.’

For believe in the name of, see comments on 3.23; the verb form used here is the present participle, the present tense expressing continuation. For Son of God see comments on 3.8.

Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The First Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .