It's amazing the stuff in the Bible that's right out there in the open, and yet seems so suddenly surprising when the Holy Spirit brings it to our attention.
So in 1 Samuel, God thoroughly warns Israel about asking for a king, right? And yet the Davidic line of kings is central to Israel, and even the concept of who the Messiah is! It seems to be an unusually strident warning, for something that God seemingly wanted to do anyway.
However, it's the details of God's warning which gives the context. The king "takes your sons" and puts them into his army, he takes them to "plow his ground" and "reap his harvest". He will "take the best of your fields, your vineyards, and your olive groves, and give them to his servants." He will take a "tenth of your seed, your vineyards, your olive groves,[...] your flocks", and give them to his servants. In fact, "you yourselves will becomes his servants."And how do the people reply? "No, but there shall be a king over us, [...] so that our king may judge us and go out before us and fight our battles."
I've heard some people interpret this passage to mean that Israel is simply rejecting God here. But in the entire Old Testament up until this point, there isn't any clear description of God as "king", with the very notable exception of the last line of the Song of Moses (after they crossed the Red Sea and the army of Pharoah was destroyed), where it says -- quite prophetically, in fact -- that "God reigns for ever and ever". Though even here, one could assume that this describes a generic reign over the entire earth.
But in this passage, God is clearly establishing the criteria and powers of a king, then hears Israel's fervent assent to it, and then later identifies himself with David (a man after God's own heart), and unites God's chosen servant -- the Messiah -- with the Davidic kingship. In later prophets this Messiah is named as "God with us", further cementing the process by which God himself is the king, who rules over the kingdom of his people.
This is why Jesus speaks so strongly of the "kingdom of God"! There's a firm connection between this passage, and the stated purpose of Jesus' ministry. He is referred to, over and over, as king of this kingdom, indeed the "king of kings". He calls people to "plow, sow, and harvest" in his fields, we offer portions of our goods, which benefit God's servants (i.e. pastors, but more generally all the saints). And we certainly join his holy army when he comes again, as "the armies of heaven, dressed in fine linen, white and pure" (Rev 19). "Even so, come quickly Lord Jesus!"
