I didn't say anything about the present active indicative. I spoke of the perfect tense. The Greek perfect verb tense indicates a past action whose results continue to the present. In this case the present was when John wrote his letter. This indicates that Jesus was still in the flesh when John wrote his letter. I'm not sure why you posted the passage from 1 Cor 15. Do you believe it somehow cancels what John said? You still have to reconcile what John said. Now you have to reconcile both passages together. However, the kingdom of God is not in Heaven so it really doesn't bear on the subject.
Even so, if we look at the passage you posted in context we can see what Paul means. In context Paul is contrasting corruption and incorruption. The earthly body and the resurrected body. When he says flesh and blood cannot inherit the kingdom, he's speaking of the present state, the corrupted state that we are now in. Only in the resurrected state can one inherit the kingdom. However, it will be physical beings that inherit the kingdom. When Jesus ascended into Heaven it was in the flesh and the angels said He will return in like manner.
9 Now when He had spoken these things, while they watched, He was taken up, and a cloud received Him out of their sight.
10 And while they looked steadfastly toward heaven as He went up, behold, two men stood by them in white apparel,
11 who also said, "Men of Galilee, why do you stand gazing up into heaven? This same Jesus, who was taken up from you into heaven, will so come in like manner as you saw Him go into heaven."
(Acts 1:9-11 NKJ)
We know that Jesus was flesh when He was resurrected because He said so.
36 Now as they said these things, Jesus Himself stood in the midst of them, and said to them, "Peace to you."
37 But they were terrified and frightened, and supposed they had seen a spirit.
38 And He said to them, "Why are you troubled? And why do doubts arise in your hearts?
39 "Behold My hands and My feet, that it is I Myself. Handle Me and see, for a spirit does not have flesh and bones as you see I have." (Lk. 24:36-39 NKJ)
There is nothing in Scripture that would indicate that Jesus is not in the flesh at present.
You said: "Jesus was still in the flesh when John wrote--" Strange that you know something that John did not know. The inspired John wrote in I Jn.3:2: "Beloved, now are we the sons of God, and it doth not yet appear what we shall be :but we know that, when he shall appear, we shall be like him; for we shall see him as he is." If the inspired John does not know, how is it that you, an uninspired man knows??
James 2:26 reads: The body apart from the spirit is dead". Now lets note which departs to be with God, the body (which is the flesh) or the spirit of man.
1. Gen.25:8: "And Abraham GAVE UP THE GHOST, (EMP. MINE, BB) and died in a good old age,--".
2. I Kings 17:22: "And the Lord heard the voice of Elijah; and the soul of the child came into him again, and he revived".
3. Gen,.35:18: And it came to pass, as her soul was departing (for she died)."
4. At the time Steven was dying, being stoned he said "Lord Jesus, receive my spirit.:" He did not say
receive my flesh.
The above examples may be extended. They are irresistible and establish beyond reasonable doubt that it is the spirit, the soul of man and not the flesh which leaves the body behind and "flies away" (Ps.90:10).
I ask, at death what left and returned to God? The flesh or the spirit? What returned to the dust? The flesh or the spirit? Hear Eccl.12:7: "Then shall the dust (the body, the flesh of man, EMP. MINE, BB) return to the earth as it was: and the SPIRIT (emp.mine,BB) shall return unto God who gave it." I ask you to provide one single verse which says th flesh leaves the body and returns to God.
You said "Jesus was still in the flesh when John wrote--" But the inspired Luke says different: "And when Jesus had cried with a loud voice, he said, Father into thy hands I commend my spirit: and having said thus, he gave up the ghost" Lk.23:46. Both Matthew and Mark say Jesus gave up his ghost (or spirit) on the cross. I Cor. 15:50 still reads "flesh and blood shall not inherit the kingdom of God".
This is all I have time for presently.
TO BE DEEP IN SCRIPTURE IS TO CEASE BEING CATHOLIC, PROTESTANT, JEW AND CALVINIST