He made a pit - The allusion here is undoubtedly to a method of hunting wild beasts which was common in ancient times. It consists in digging a pit-fall, and covering it over with brush and grass so as to deceive the animals, and then enclosing them and driving them into it. See the notes at Isaiah 24:17.
And digged it - And hollowed it out so as to be large enough to contain his prey, and so deep that he could not escape if he fell into it. The idea is, that the enemy here referred to had laid a secret and artful plan to destroy others. He meant that they should not be aware of his plan until the mischief came suddenly upon them. He was preparing to ruin them, and supposed that he was certain of his prey.
And is fallen into the ditch which he made - Into the pit-fall which he had constructed for others; as if a man who had made a pit-fall for wild beasts had himself fallen into it, and could not extricate himself. That is, he had been snared in his own devices; his cunning had recoiled on himself, and instead of bringing ruin on others he had only managed to bring it on himself. See this sentiment illustrated in the notes at Job 5:13. A remarkable instance of the kind may be found in Esther (Est. 5–7), in the case of Haman. Indeed, such things are not uncommon in the world, where the cunning and the crafty are involved in the consequences of their own plans, and are taken in meshes from which they cannot free themselves. A straightforward course is easy, and men are safe in it; but it requires more skill than most men are endowed with to manage a crooked and crafty policy safely, or so as to be safe themselves in pursuing such a course. A spider will weave a web for flies with no danger to himself, for he is made for that, and acts as if he understood all the intricacies of his own web, and may move safely over it in every direction; but man was made to accomplish his purposes in an open and upright way, not by fraud and deceit; hence, when he undertakes a tortuous and crooked course - a plan of secret and scheming policy - in order to ruin others, it often becomes unmanageable by his own skill, or is suddenly sprung upon himself. No one can overvalue a straightforward course in its influence on our ultimate happiness; no one can overestimate the guilt and danger of a crooked and secret policy in devising plans of evil.