He said this after his resurrection before he ascended to heaven. Yes, Jesus is in heaven now, and he said "All authority has been given me in heaven and on the earth." I don't know what that means to you, but I would think it means all authority was given to Jesus in heaven AND on the earth. That's both heaven and earth. All authority has been given to him in heaven and earth.
I already told you what I think that means. All authority was given to Jesus
while He was on earth, but now Jesus is in heaven.
Jesus has authority in heaven, but Jesus no longer has any authority on earth.
Jesus never said that all authority was given to him on earth for all of time. When Jesus said that He was referring to the time that He was on earth.
Further, 1 Corinthians 15 explains about the time when Jesus will hand over the Kingdom to his God and Father, when he has brought to nothing all government and all authority and power.
This goes on to explain that Jesus will rule as king until God has put all enemies under his feet. And after that, Jesus will then subject himself to the One who subjected all things to him, so that God may be all things to everyone.
1 Corinthians 15 King James Version (KJV)
23 But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming.
24 Then cometh the end, when
he shall have delivered up the kingdom to God, even the Father; when
he shall have put down all rule and all authority and power.
25 For
he must reign, till he hath put all enemies under his feet.
26 The last enemy that shall be destroyed is death.
27 For
he hath put all things under his feet. But when
he saith all things are put under him, it is manifest that
he is excepted, which did put all things under
him.
28
And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
Verse 28 says: And when all things shall be subdued unto him, then shall the Son also himself be subject unto him.
he and
him in verses 25-28 cannot cannot be Jesus since Jesus was the Son. and Jesus cannot be subject to Himself.
The Son is going to be subject to him, whoever he is.
In sum, whoever is going to reign will not be Jesus.