See the margin. The meaning is "Thy joy will be suicidal, the wrath of the righteous Judge will be turned upon thee, as the greater offender, and thou wilt have to bear a worse evil than that which thou exultest in."

And he turn away his wrath from him - Wrath is here taken for the effect of wrath, punishment; and the meaning must be as paraphrased above - lest he take the punishment from him, and inflict it upon thee. And in this way Coverdale understood it: "Lest the Lorde be angry, and turn his wrath from him unto thee." Or we may understand it thus: Lest the Lord inflict on thee a similar punishment; for if thou get into his spirit, rejoicing in the calamities of another, thou deservest punishment.

Lest the LORD see [it], and it displease him, and he turn away his wrath (f) from him.
(f) To be avenged on you.

Lest the Lord see it, and it displease him,.... Who sees all things, not only external actions, but the heart, and the inward motions of it; and though men may hide the pleasure they feel at the misery of an enemy from others, they cannot hide it from the Lord; nor is this said by way of doubt, but as a certain thing; and which the Lord not barely sees, but takes notice of, and to such a degree as to resent it, and show his displeasure at it by taking the following step;
and he turn away his wrath from him; remove the effects of it, raise him out of his fallen and distressed condition, and restore him to his former prosperous one; and not only so, but turn it upon thee, as Gersom supplies the words, and not amiss; so that there is a strange and sudden change of circumstances; thou that was pleasing thyself with the distress of thine enemy art fallen into the same, and he is delivered out of it; which must be a double affliction to such a man; so that by rejoicing at an enemy, he is doing his enemy good and himself hurt; see Proverbs 17:5.

From him - Understand, upon thee, which is implied in the Hebrew phrase.