name of R. Johanan: When a man has lived the greatest part of his life without having sinned, he will sin no more, for they will guard him Above, and this he infers from the above passage. The disciples of R. Shila have said: When a man has had occasion to commit a sin once and twice, and he escapes committing it, he will be guarded Above from sinning. They infer it from the same verse. Resh Lakish said: It is written [Prov. iii. 34]: "The mockers He will mock, but to the modest He will give grace." From this we can infer: If one wishes to defile himself (to sin) the door is opened to him; but he who comes to purify himself, he is assisted. The disciples of R. Ishmael have told a parable in reference to this: When one sells both naphtha and perfumes, when one arrives to buy naphtha, he saith to him: "Measure the quantity you need"; but if one arrives to buy perfumes, he says: "Wait, we will both measure it, and contract the odor." The same disciples taught: A sin stops up a man's heart, as it is written [Lev. xi. 43]: "And ye shall not make yourselves unclean with them, that ye should be defiled thereby." Do not read ונטמאתם but ונטמטם (stop up).
The rabbis taught: This verse signifies that when a man defiles himself a little here below, Above he is defiled much; and if he defiles himself in this world, he is defiled in the world to come. And it is written [ibid. 44]: "Ye shall sanctify yourselves, and be holy." When a man sanctifies himself a little here below, he is sanctified much Above, and when he sanctifies himself in this world, he is sanctified in the world to come.
