You are confusing the world with the earth. Jesus always did have the authority, He could have turned stones to bread or called down legions of angels. But the issue is not of this world. Yet He remains Mediator even in the world, until the times of the gentiles are fulfilled.
In His own words, Jesus said He had come "but only for the house of Israel", and then when all things had been fulfilled, He said "It is finished."
After this, Jesus, knowing that all things were now accomplished, that the Scripture might be fulfilled, said, “I thirst!” 29 Now a vessel full of sour wine was sitting there; and they filled a sponge with sour wine, put it on hyssop, and put it to His mouth. 30 So when Jesus had received the sour wine, He said, “It is finished!” And bowing His head, He gave up His spirit. John 19:28-30
When Christ said, "it is finished" what He came to do was finished, the redeeming of man.
When Christ came to Israel and offered them the Kingdom, they were to introduce their Messiah to the world, but they rejected Him. Then Christ turned to Paul and sent him to the Gentiles to introduce Christ to the world. The 11 apostles, when driven from Jerusalem with James already being killed, they followed Paul in taking the Gospel to the Gentiles.
Christ built His Church from these converts, to bear the responsibility of spreading the Gospel. But I have shown you, God is far from finished with His chosen people of Israel. Their glory is coming in the near future.
Jeremiah 31:1-9
"At the same time, saith the Lord, will I be the God of all the families of Israel, and they shall be my people.
2 Thus saith the Lord, The people which were left of the sword found grace in the wilderness; even Israel, when I went to cause him to rest.
3 The Lord hath appeared of old unto me, saying, Yea, I have loved thee with an everlasting love: therefore with lovingkindness have I drawn thee.
4 Again I will build thee, and thou shalt be built, O virgin of Israel: thou shalt again be adorned with thy tabrets, and shalt go forth in the dances of them that make merry.
5 Thou shalt yet plant vines upon the mountains of Samaria: the planters shall plant, and shall eat them as common things.
6 For there shall be a day, that the watchmen upon the mount Ephraim shall cry, Arise ye, and let us go up to Zion unto the Lord our God.
7 For thus saith the Lord; Sing with gladness for Jacob, and shout among the chief of the nations: publish ye, praise ye, and say, O Lord, save thy people, the remnant of Israel.
8 Behold, I will bring them from the north country, and gather them from the coasts of the earth, and with them the blind and the lame, the woman with child and her that travaileth with child together: a great company shall return thither.
9 They shall come with weeping, and with supplications will I lead them: I will cause them to walk by the rivers of waters in a straight way, wherein they shall not stumble: for I am a father to Israel, and Ephraim is my firstborn.