A.T. Robertson Commentary John 14:1

"Let not your heart be troubled: believe in God, believe also in me." — John 14:1 (ASV)

Let not your heart be troubled (μη ταρασσεσθω υμων η καρδια). Not here the physical organ of life (Luke 21:34), but the seat of spiritual life (πνευμα, ψυχη), the centre of feeling and faith (Romans 10:10), "the focus of the religious life" (Vincent) as in Mt 22:37. See these words repeated in 14:27. Jesus knew what it was to have a "troubled" heart (11:33; 13:31) where ταρασσω is used of him. Plainly the hearts of the disciples were tossed like waves in the wind by the words of Jesus in 13:38.

Ye believe... believe also (πιστευετε... κα πιστευετε). So translated as present active indicative plural second person and present active imperative of πιστευω. The form is the same. Both may be indicative (ye believe... and ye believe), both may be imperative (believe... and believe or believe also), the first may be indicative (ye believe) and the second imperative (believe also), the first may be imperative (keep on believing) and the second indicative (and ye do believe, this less likely). Probably both are imperatives , "keep on believing in God and in me."