Acts 1:8 reads:
ALLA LHMYESQE DUNAMIN EPELQONTOS TOU hAGIOU PNEUMATOS EF' hUMAS KAI ESESQE MOU MARTURES EN TE IEROUSALHM KAI EN PASAi THi IOUDAIAi KAI SAMARIAi KAI hEWS ESXATOU THS GHS.
While studying the NT use of the future tense, I ran across something I had not thought about before. Daniel B. Wallace says that Acts 1:8 is an example of the predictive future. But he goes on to point out that the second future in the passage, namely, LHMYESQE DUNAMIN EPELQONTOS TOU hAGIOU PNEUMATOS EF' hUMAS KAI ESESQE MOU MARTURES, may be imperatival (Wallace, GGBB, 568). In fact, John Polhill contends that the future tense in Acts 1:8 does have "an imperatival sense" (Polhill, Acts, 85). He words the passage: "you will [must] receive power" and "you WILL be my witnesses."
Morphologically, the futures in Acts 1:8 could be construed as predictives or imperativals.