‘And while they were looking steadfastly into heaven as he went, behold, two men stood by them in white clothing, who also said, “You men of Galilee, why do you stand looking into heaven? This Jesus, who was received up from you into heaven shall so come in like manner as you beheld him going into heaven.” '
The significance of this event is further emphasised by the appearance of two men in white clothing. Through them a deliberate message is conveyed to the disciples as they quite understandably continued to gaze up into the now empty sky, unable to fully take in what was happening. Some of them had probably already been ready waiting for the call to arms so that their risen Messiah could lead them against the Romans. (That was what their earlier question had been all about). Now they knew that it was not to be, and that they were standing on the verge of something totally new, and they were stunned, and probably felt completely bereft. They would know that they were going to have to totally rethink their position in the light of what Jesus had said during the forty days in which He had appeared to them.
The two men, who by their description as being ‘in white clothing' are depicted as messengers (angels) from God (it was the recognised way of describing such - Matthew 28:3; Mark 16:5; John 20:12), gently rebuked them for standing there gazing up into heaven. This was no time to stand and stare. It was time for them to recognise that one day He would return in the same way as they had seen Him go (personally), and that He would then expect them to have completed the task that He had given them. He would come personally to call them to account and He would not want to come and find them either sleeping or staring upwards. God's prime concern was now that they take out to all the world their witness about Him.
Jesus had now, as it were, gone into a ‘far country', but one day He would return, and in that day they would have to give full account of all that they had done (Luke 19:12-27).
It should here be noted that with one blow Jesus had transformed all their thinking. He had told them that from now on their thoughts were to be concentrated simply on one question, how can we best take our witness to the world and proclaim Christ, and in what form shall we take it? There would (hopefully) be no more thoughts about earthly kingdoms and fighting and force of arms. As ever Jesus with a few quiet words had removed a host of misconceptions. Whatever their thoughts and expectations had been they had now all to be set aside, without any need for argument, and replaced by a simple mission (simple in concept not in application) which would take up the remainder of their lives (and ours too). How seriously they took it comes out in Acts 6:4.
Speculation as to whether the two men in white were Moses and Elijah is totally unhelpful. It produces fictitious ‘blessed thoughts' not based on fact. We must beware of trying to add to Scripture.