In Proposition 84, George Peters states:
“As this Kingdom is specially given to the Son of Man as the result of his obedience, sufferings, and death, it must be something different from His Divine nature, or from “piety”, “religion”, “God’s reign in the heart”, etc.”
Man has demonstrated at least to some degree elements of piety, has had religion and religious tendencies, and for the believer, God resides in their hearts via the Holy Spirit. Based on those facts, the status of Jesus as the Son of Man has a much greater reality than what can be applied to normal humanity. He came and did something no man could do, namely to fully obey God’s commands, to suffer as the spotless, sinless Lamb of God to be the atonement for our sin. This is one of the fundamental truths behind the theological concept of the active obedience of Jesus. The Son of Man is given the Kingdom because of his active obedience on earth, something far more than simply being pious or religious which is about all man in his sinful nature can lay claim.
The most notable observation Peters presents in Proposition 84 is the following:
“This evinces what the covenant, etc., demands, viz.: a Ruler, who is such in virtue also of His humanity; and includes, that this Ruler has shown what no other Theocratic Ruler can do, His perfect adaptability for the position, i.e. to carry out the Divine Will in government. Keeping in view the goal of Theocratic government and its requirements, we find in the honorable obedience of Christ the most ample and satisfactory assurance that in His occupancy of the Davidic throne and Kingdom, He will indeed be a truthful and stable Representative of God. Therefore Peter says, 1 Peter 1:21, etc.”
The demands of the covenant required the Messiah to come as the spotless Lamb. His active obedience and death on our behalf merits Him the status if you will of being the Theocratic Ruler. No other individual in human history (past, present, or future) has the qualifications required to sit on the throne of David. Only Jesus meets all of the standards within the covenant and thus, as the Son of Man (and Son of God), the throne is his for all eternity and he will occupy it at the time deemed appropriate by the Father.