So what is the reign of God exactly? Is that the same as the kingdom of God? And by seeing, does Jesus mean with human eyes or spiritual eyes?
Paper 170, section 4 is a good place to look for more I think, I do believe he was talking about God’s reign in believers’ lives, that some of the believers listening to him would feel that reign “in great power” for themselves before they died:
“Jesus never gave a precise definition of the kingdom. At one time he would discourse on one phase of the kingdom, and at another time he would discuss a different aspect of the brotherhood of God’s reign in the hearts of men. In the course of this Sabbath afternoon’s sermon Jesus noted no less than five phases, or epochs, of the kingdom, and they were:
1. The personal and inward experience of the spiritual life of the fellowship of the individual believer with God the Father.
2. The enlarging brotherhood of gospel believers, the social aspects of the enhanced morals and quickened ethics resulting from the reign of God’s spirit in the hearts of individual believers.
3. The supermortal brotherhood of invisible spiritual beings which prevails on earth and in heaven, the superhuman kingdom of God.
4. The prospect of the more perfect fulfillment of the will of God, the advance toward the dawn of a new social order in connection with improved spiritual living—the next age of man.
5. The kingdom in its fullness, the future spiritual age of light and life on earth.”