In line with what I quoted earlier from Charles Spurgeon, consider this quotation from the Christian philosopher Cornelius Van Til:
The Kingdom of God as Man’s Summum Bonum
We need all this background in order to understand what is meant by saying that the kingdom of God is man’s summum bonum. By this term kingdom of God we mean the realized program of God for man. We would think of man as (a) adopting for himself this program of God as his own ideal and as (b) setting and keeping his powers in motion in order to reach that goal that has been set for him and that he has set for himself. We propose then briefly to look at this program which God has set for man and which man should have set for himself.
The most important aspect of this program is surely that man should realize himself as God’s vicegerent in history. Man was created God’s vicegerent and he must realize himself as God’s vicegerent. There is no contradiction between these two statements. Man was created a character and yet had to make himself ever more of a character. So we may say that man was created a king in order that he might become more of a king than he was. We may see what this means first in the individual, and secondly, for society.