Matthew 8:4
And Jesus said to him, See that you say nothing to anyone, but go, show yourself to the priest and offer the gift that Moses commanded, for a proof to them. The silence command and the Mosaic compliance command belong together: the healing is not to be a public spectacle but a private sign. Showing himself to the priest and offering the Leviticus 14 gift is the proper completion of the restoration process within the covenant law — Jesus is not replacing the Torah but fulfilling it, as he said in Matthew 5:17. The for a proof to them (the priests) is the witness that the kingdom has arrived: the priests who examine the healed leper are being confronted with evidence that something unprecedented has occurred.