Deuteronomy 18:20-22 concerns the false prophet. A false prophet was one who spoke a word presumptuously in God's name which God did not command him to speak or who spoke in the name of other gods (v. 20a). Such a prophet was to be put to death (v. 20b). When a prophet spoke in the name of Jehovah and the thing did not happen, that was the thing which Jehovah had not spoken (v. 22).
The children of Israel were to set apart cities of refuge (19:1-13), cities into which those who had killed others accidentally could escape. These cities signify God's preparing Christ as a refuge for all sinners.
The numbers related to the refuge cities are significant. For convenience, there were to be six refuge cities, three on either side of the Jordan. The number six signifies man, who was created on the sixth day. The number three signifies the Triune God. The Triune God has come in incarnation to be our refuge; He is for us. Furthermore, the number two, implied by the fact that there were cities on the two sides of the Jordan, signifies testimony or witness. The Triune God embodied in the incarnated Christ has come to the place where we live to be our refuge. Instead of asking us to come where He is, He came to where we are. This is the reason that in preaching the gospel, we should not ask people to come to us; rather, we should bring the gospel to them. To ask others to come to us is contrary to God's ordination. (For details on the refuge cities, please see the life-study on Numbers 35:9-34.)