Commentary: "What, then, is to be done with respect to the lustful heart and eye? The answer is found in verses 29, 30. So if your right eye lures you into sin, pluck it out and fling it away from you. It is better that you lose one of your members than that your whole body be thrown into hell. And if your right hand lures you into sin, cut it off and fling it away from you. It is better that you lose one of your members than that your whole body go down into hell. This command must not be taken literally, for even if a person should literally pluck out his right eye he would still be able to sin with his left eye. Jesus has himself supplied us with the key to its interpretation, namely, in Matt. 18:7–9, where in slightly different form this command is repeated. From that passage it follows clearly that the eye and the hand that lead a person into sin symbolize and represent “occasions of stumbling,” or if one prefers, enticements to do wrong, beguiling allurements. The general meaning of the passage, then, is this: “Take drastic action in getting rid of whatever in the natural course of events will tempt you into sin.” In the present connection it is especially the sin against the seventh commandment that is in view.

More in detail, it would seem that the following lessons are taught here:

a. The present is not our only life. We are destined for eternity. Note: “… than that your whole body be thrown into—or go down into—hell.”
b. Nothing, no matter how precious it may seem to us at the moment—think of the right eye and the right hand—should be allowed to doom our glorious destiny.
c. Sin, being a very destructive force, must not be pampered. It must be “put to death” (Col. 3:5). Temptation should be flung aside immediately and decisively. Dillydallying is deadly. Halfway measures work havoc. The surgery must be radical. Right at this very moment and without any vacillation the obscene book should be burned, the scandalous picture destroyed, the soul-destroying film condemned, the sinister yet very intimate social tie broken, and the baneful habit discarded. In the struggle against sin the believer must fight hard. Shadow-boxing will never do (I Cor. 9:27).

Of course, these destructive, and in that sense negative, actions will never succeed apart from the powerful sanctifying and transforming operation of God’s Spirit in heart and life. Throughout the sermon therefore Jesus emphasizes the positive. He has done it just now (see verses 23–26), previously in the beatitudes (5:1 ff.), and will continue to do it (5:37, 39–42, 44–48; etc. See also Luke 11:24–26). The beautiful passage found in II Cor. 6:17, 18, a composite quotation from the Old Testament, gives the sense as follows:

“Wherefore come out from among them and be separate, says the Lord, and touch no unclean thing; and I will receive you. And I will be to you a Father; and you shall be to me sons and daughters” (II Cor. 6:17, 18; see also verses 14–16).

By saying, “It is better that you lose one of your members,” etc. Jesus emphasizes how incomparably more necessary and far better it is to prepare for eternity than to enjoy (?) the sinful pleasures of this life. Without in any way encouraging or even permitting anyone literally to mutilate himself he is saying that it is surely better to go through the present life maimed in body than, with the whole body still sound and unharmed, to be thrust into Gehenna (“hell”). See also on 10:28 and 16:26." - William Hendriksen