Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
The following commentary covers Chapters 21 and 22.
Chapter 21 specially presents what becomes the priests as set apart for Jehovah: this more intimate nearness supposed a conduct corresponding with it. All in their state must be fit for God's presence. So it is with us. Chapter 22. If there was, through weakness or neglect, anything unbecoming this nearness, they were to keep at a distance. Consequently there were things of which the priests, and those of their families in priestly separation, alone could eat. It is the same with us: there are things of the spiritual food of Christ, offered to God, upon which we can only feed, inasmuch as the heart is really separated unto Him, by the power of the Spirit. The offerings themselves must be pure, and such as become the eyes of God to whom they are presented, and a right appreciation of His majesty, and of our relationship with Him. All this indeed is found in Christ. No hardness of nature is allowed, but holiness. In what is connected with our own joy before God, holiness must be maintained in what is offered.
In chapter 20, where they are forbidden to follow the brutal and superstitious customs of idolatry (to which Satan had degraded man) and are warned against all impurity, which indeed was always inseparable from it, and for which the influence of the devil gave license, we have this simple and beautiful exposition of the principle which was to govern them: "Sanctify yourselves, therefore, and be ye holy: for I am Jehovah your God. And ye shall keep my statutes, and do them: I am Jehovah which sanctify you." They are bound to holiness and to sanctify themselves practically, because they are in the house, and the Master of it is holy. Sanctification supposed that they were in an acknowledged relationship with God, who will have the inmates of His house clean according to His own cleanness. But then His word was to be the rule. They were to obey Him in His directions, for it was He who was separating them to Himself. This is a very instructive word as to the standard of all our thoughts with regard to that. If any are in my house, I will have them clean, because they are there; those outside are no concern of mine [See Note #1]. Then it was Jehovah who was separating them for that. There are interesting instructions with regard to what the priests ate, which we shall find again in the following book, and consider when we come to it.
Note #1
I do not speak of responsibility or mercy here.