The first part of this verse is literally “If you know these things….” Here again, as in verse 14, the “if” clause in Greek states a condition that is true to fact. On this basis Good News Translation transforms the “if” clause into a statement: Now that you know this truth (Jerusalem Bible “Now that you know this…”). This truth translates the more generic “these things” of the Greek text. Although the antecedent of “these things” is not altogether clear, it is best taken as a reference to the words of Jesus in verses 13-16.
In some languages it is not possible to speak of this truth; that is, something which is true may not be spoken of simply as an abstract in a nominal (or noun) form. However, one can say “Now that you know this” or “Now that you know this is true” or “Now that you realize that what I have said is true.”
How happy you will be is literally “you are happy (Greek makarios).” The Greek adjective used here is the same one used in each of the Beatitudes. It occurs once again in John’s Gospel (20.29). It is a difficult word to translate with precision, but most modern English translations render it as either “happy” or “blessed.” Die Bibel im heutigen Deutsch renders “joy without end.” In biblical thought the ideas of “blessed” and “happy” are related, but there is a slight difference in focus. “Blessed” focuses attention on the source of the benefit, that it has come from God, while “happy” describes the state of the person who receives the benefit. In the present passage, as in most other New Testament passages where this Greek word occurs, the focus is upon the subjective state of happiness shared by persons who have received God’s blessing. For this reason, the translation “happy” is preferable to “blessed.”
If you put it into practice is literally “if you do these things,” referring to this truth at the beginning of the verse (literally “these things”). Jerusalem Bible translates the two clauses as “happiness will be yours if you behave accordingly,” while New English Bible renders “happy are you if you act upon it”; and Phillips has “you will find your happiness in doing them.”
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 .