[Acts 1:9] shows that the disciples were "looking on" and saw him "lifted up and a cloud caught him up from their vision" (v. 9). They could hardly have been looking at a spirit, which by definition is incorporeal, not with human eyes at least, and Christ had told them once before, "Behold my hands and my feet, that it is I myself: handle me, and see; for a spirit hath not flesh and bones, as ye see me have" (Luke 24:39). [Walter Martin, The Kingdom of the Cults, Revised, Updated, and Expanded Edition, Ravi Zacharias, General Ed. (Bloomington, Minn.: Bethany House Publishers, 2003), page 102; compare also page 121.]In a footnote to the word "incorporeal" Martin writes, "Even angels have to take a human form in order to be seen (Genesis 19:1-2)," and so it is a genuine mystery why Martin did not see that Jesus, since his resurrection as a "spirit" (1 Corinthians 15:45 [see discussion below]), could also have taken on various human forms, including the one he chose in Acts Chapter 1, but without requiring him (or the angels in Genesis 19) to actually have a real human body apart from such physical manifestations.
Where it concerns Jesus' words in Luke 24:39, here is the text together with verses 36-38 and 40-43 according to the New Revised Standard Version (with my added underlining):
While they were talking about this, Jesus himself stood among them and said to them, "Peace be with you." They were startled and terrified, and thought that they were seeing a ghost. He said to them, "Why are you frightened, and why do doubts arise in your hearts? Look at my hands and my feet; see that it is I myself. Touch me and see; for a ghost does not have flesh and bones as you see that I have." And when he had said this, he showed them his hands and his feet. While in their joy they were disbelieving and still wondering, he said to them, "Have you anything here to eat?" They gave him a piece of broiled fish, and he took it and ate in their presence.
If Jesus is correct, namely, that "a spirit does not have flesh and bones," then the body which he manifested to his followers according to Luke 24:39 was not the same body in which he was raised to life. Note what is written concerning this raising to life, that is, the actual resurrection of Jesus of Nazareth from the dead according to 1 Corinthians 15:35-45 (with my underlining added):
But someone may ask, "How are the dead raised? With what kind of body will they come?" How foolish! What you sow does not come to life unless it dies. When you sow, you do not plant the body that will be, but just a seed, perhaps of wheat or of something else. But God gives it a body as he has determined, and to each kind of seed he gives its own body. All flesh is not the same: Men have one kind of flesh, animals have another, birds another and fish another. There are also heavenly bodies and there are earthly bodies; but the splendor of the heavenly bodies is one kind, and the splendor of the earthly bodies is another. The sun has one kind of splendor, the moon another and the stars another; and star differs from star in splendor. So will it be with the resurrection of the dead. The body that is sown is perishable, it is raised imperishable; it is sown in dishonor, it is raised in glory; it is sown in weakness, it is raised in power; it is sown a natural body, it is raised a spiritual body. If there is a natural body, there is also a spiritual body. So it is written: "The first man Adam became a living being"; the last Adam, a life-giving spirit [Greek: pneuma].
And I turned to see the voice that was speaking with me, and, having turned, I saw seven golden lampstands, and in the midst of the lampstands someone like a son of man, clothed with a garment that reached down to the feet, and girded at the breasts with a golden girdle. Moreover, his head and his hair were white as white wool, as snow, and his eyes as a fiery flame; and his feet were like fine copper when glowing in a furnace; and his voice was as the sound of many waters. And he had in his right hand seven stars, and out of his mouth a sharp, long two-edged sword was protruding, and his countenance was as the sun when it shines in its power.
Here we have a clear description of what Jesus’ heavenly body looks like to humans. Jesus’ “head” and his “hair” are said to be “white as wool, as snow, and his eyes as a fiery flame.” His feet are “like fine copper when glowing in a furnace” and “his voice was the sound of many waters.” Finally, his “countenance was as the sun when it shines in its power.” This is a far cry from the human forms Jesus took on after his resurrection! Revelation 2:18 also describes the heavenly Jesus in similar terms, where it says he has “eyes like a fiery flame, and his feet are like fine copper.” These descriptions are also very similar to the angel in Revelation 10:1, whose “face was as the sun, and his feet were as fiery pillars.” It is little wonder, then, that the apostle Paul refers to Jesus as ‘not a man’ in Galatians 1:12.