Why does "put all enemies under His feet" have to mean becoming christian via the gospel? Does "death" become subjected or is it destroyed, you see where I'm going with this?
I do see where you are going, and it is my firm belief that nothing but the personal appearing of our Lord Jesus Christ will bring perfect restoration and do away with the element of wickedness in creation. But in commissioning His servants to disciple all nations, King Jesus did not make any qualification with respect to His second coming, but promised that He would be with them to the end of the world. Hence, it should not be an issue as to what shall come to pass in the Father's good pleasure prior to the coming of Christ; the issue is, what ought the church to be striving towards with the gracious presence of Christ on her side.