In Greek the clause But if I do does not have an object expressed, but Good News Translation and some other translations express the object as them, referring back to deeds in verse 37.
You should at least believe my deeds is literally “believe the works” (Revised Standard Version). In Greek the verb believe is imperative, but it expresses more an appeal than a command, and so Good News Translation translates you should … believe. The inclusion of the adverbial phrase at least (so also Jerusalem Bible and Die Bibel im heutigen Deutsch) helps to indicate more fully the connotation of Jesus’ words. Finally, “the works” is obviously a reference to Jesus’ works, and so it is legitimate to translate my deeds (so New English Bible). In the Greek of this verse, forms of the verb “to know” are used twice. The first is an aorist, meaning “that you may begin to know,” while the second is a present meaning “and that you may keep on knowing.” Good News Translation combines the two verbs into one and translates that you may know once and for all. Jerusalem Bible also uses one verb plus an adverbial expression, “then you will know for sure.” The decision of Good News Translation and Jerusalem Bible is certainly valid, because the two verbs are apparently used simply to reinforce one another. To translate by two different verbs meaning “to know,” as most translators do, is not necessary.
The last words of this verse (that the Father is in me, and I am in the Father) refer back to the words of Jesus in verse 30 that initiated this controversy between him and the Jews. It is, of course, an essential theme of the Gospel of John that Jesus and the Father are one. Die Bibel im heutigen Deutsch has “that the Father lives in me, and I live in the Father.”
The grammatical structure of verse 38 is rather complex. It consists of several clauses bound closely together. The first is a condition, if I do them; the second, a concession, even though you do not believe me; the third is the main clause, you should at least believe my works; the fourth is a purpose clause, in order that you may know, which has as its content object the indirect statement, that the Father is in me, and I am in the Father. In some languages it is not possible to combine so many complex clausal relations within a single sentence. But this rather complex grouping may be broken up as follows: “But if I do my Father’s works, you should at least believe what I have done. You should believe these works even though you do not believe me. You should believe in what I have done in order that you may know once and for all that the Father is in me and I am in the Father.” In some languages, however, it is difficult to use the same type of expression in speaking of “believing a person” and “believing works.” “To believe a person” would mean “to trust what a person has said” or “to believe that what a person has said is true.” On the other hand, “believe my works” may be more or less equivalent to “take seriously my works” or “have confidence in what I say because of what I have done.”
That the Father is in me, and I am in the Father may require modification because of the problem of a so-called possessive relation with Father, for example, “that my Father is in me and I am in my Father.” However, this expression may seem meaningless in some languages, and therefore one may say “that my Father and I are completely joined together as one” or “that my Father and I are just like one person.” This expression is therefore equivalent to the expression “my Father and I are one.”
Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .