NOTES for Sa2 7:12-13
The covenant that God concluded with David played a major role in the becoming and the development of the yahvist messianic traditions. At first, as seen, it is about a union-covenant with David, as the founder of the dynasty of Jerusalem. There is nothing surprising here: its history began only with David, if is taken into consideration the fact that neither Israel, nor the Judea were never absolute monarchies, protecting the power to the successors of David would have been something very difficult without God's help. But it is only the earthly historic measure of the covenant concluded with David. Already in the time of the late prophets, they begin to look at it[ the covenant] a little bit differently.
It is not surprising: because the image of the Kingdom of God changes considerably thanks to the sermon, above all, of Isaiah of Jerusalem. Before, the Kingdom was perceived, as a reality purely earthly, politico-religious. And the covenant with David was seen as a guarantee of the fact that one day this politico-religious project, born among the leaders of the movement of the very first prophets, will come true.
But it was already revealed to Isaiah that the Kingdom of God will not be connected with the reforms only, that it is necessary to speak here about the direct intervention of God, about a special revelation, about the plenitude of His presence, such that the people of God did not know before.
Then the image of the ruler of the Kingdom of God changes: it is not longer already a simple "anointed one", as were blessed by the prophets or the priests all the kings of Israel, and after of Judah, they began to look at him, as a special servant of God, a participant in the implementation of His plans, maybe even endowed with the extraordinary capacities - brief, as a anointed one with the capital letter, the Messiah.
And then will begin the gradual transformation of the image of this semi-mythical Messiah into the image of a real Messiah, the One, of Whom the books of the New Testament tell us about. The transformations that will take more than a century, ending only in the minds of those who will meet with Him personally and will join His Kingdom.