In 13.38 Jesus was addressing Peter; in 14.1 he is addressing all his disciples. The Greek of 14.1 clearly indicates this shift: “Do not let your (plural) heart be troubled.” Most translators indicate the change in audience simply by rendering “heart” as “hearts” (New American Bible “Do not let your hearts be troubled”). Good News Translation marks the change explicitly by including the information Jesus told them, and Die Bibel im heutigen Deutsch by “Then Jesus said to them all.” Jerusalem Bible calls attention to the transition in a footnote. However, this kind of transition is better made explicit in the text, for otherwise the persons who hear the passage read may not correctly identify the person addressed. Furthermore, many readers probably do not read the footnotes. Then, too, since Chapter 14 is frequently read as a unit, it is important to indicate the persons to whom Jesus is speaking at the very outset of the chapter. It may be useful to indicate this fact quite clearly by saying “Jesus told his disciples.”
On the use of the phrase be worried and upset, see the comments at 11.33.
In both of its occurrences the verb believe may be either imperative or indicative, since the Greek forms are the same. Good News Translation, together with most translations, takes both of them as imperatives (Believe in God, and believe also in me); Good News Translation alternative reading translates the first as indicative and the second as imperative (“You believe in God, believe also in me”). A third possible combination would be to render them both as indicatives: “You believe in God, and you also believe in me.” In favor of the choice accepted by Good News Translation is the observation that the first verb in this verse (Do not be worried and upset) is a specifically imperative form in Greek. In this context Believe in me must be understood in the sense of “put your confidence in me” or “trust in me” or “trust yourself to me.”
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 .