A certain man before him - In what way he came there we know not. He might have been one of the Pharisee's family, or might have been placed there by the Pharisees to see whether he would heal him. This last supposition is not improbable, since it is said in Luke 14:1 that they watched him.
The dropsy - A disease produced by the accumulation of water in various parts of the body; very distressing, and commonly incurable.

The dropsy - Ὑδρωπικος, dropsical; from ὑδωρ, water, and ωψ, the countenance, because in this disorder the face of the patient is often very much bloated. Probably the insidious Pharisee had brought this dropsical man to the place, not doubting that our Lord's eye would affect his heart, and that he would instantly cure him; and then he could most plausibly accuse him for a breach of the Sabbath. If this were the case, and it is likely, how deep must have been the perfidy and malice of the Pharisee!

And behold, there was a certain man before him,.... Who sat just before him, as he was at table; who either came there of himself, in order to receive a cure; or rather, since it was in a private house, and he at table too, was brought and set there on purpose by the Pharisees, to try whether Christ would heal him on the sabbath day, that they might have somewhat against him; which they doubted not but he would do, knowing his compassionate and beneficent disposition to do good to creatures in distress, whenever he had an opportunity:
which had the dropsy: or "gathered waters", as the Syriac version renders it; was filled with water, which is the nature of that disease, and distinguishes it from what is called the dry dropsy: this disease is a preternatural collection of serum, or water in some part of the body; or a too great proportion thereof in the blood. The "dropsy" acquires different names, from the different parts it afflicts, or the different parts the waters are collected in; that of the "abdomen", or lower belly, called simply and absolutely "dropsy", is particularly denominated "ascites"; that of the whole habit of the body, "anasarca", or "leucophlegmatia"; that of the head, "hydrocephalus"; that of the scrotum, "hydrocele".---There is also a species of this disease, supposed to be caused instead of water, by a collection of wind, called "tympanites"; and by Hippocrates, the "dry dropsy": we also meet with dropsies of the breast, pericardium, uterus, ovaries, &c. The causes of dropsies in general, are whatever may obstruct the serous part of the blood, so as to make it stagnate in the vessels; or burst the vessels themselves, so as to let the blood out among the membranes; or weaken and relax the tone of the vessels; or this the blood, and make it watery; or lessen perspiration. These causes are various, viz. sometimes acute diseases, scirrhous tumours of any of the more noble viscera, excessive evacuations, particularly haemorrhages, hard drinking, &c. The "ascites", or "water dropsy" of the "abdomen", is the most usual case, and what we particularly call the "dropsy": its symptoms are tumours, first of the feet and legs, and afterwards of the "abdomen." which keep continually growing; and if the belly be struck or shook, there is heard a quashing of water: add to this, three other attendants, viz. a dyspnoea, intense thirst, and sparing urine; with which may be numbered heaviness, listlessness, costiveness, a light fever, and an emaciation of the body (i). Such we must suppose to be the case of this man, and that he was now in such a condition, as to be thought incurable.
(i) Chamber's Cyclopaedia on the word "Dropsy".

HEALING OF A DROPSICAL MAN, AND MANIFOLD TEACHINGS AT A SABBATH FEAST. (Luke 14:1-24)
man before him--not one of the company, since this was apparently before the guests sat down, and probably the man came in hope of a cure, though not expressly soliciting it [DE WETTE].

A certain man who had the dropsy. Either a guest or one who came to be healed.
Is it lawful? Conscious that they were watching him, he asked them a question which they declined to answer. The "tradition" said it was unlawful.
Which of you shall have an ass? See notes on Matthew 12:11.

There was a certain man before him - It does not appear that he was come thither with any insidious design. Probably he came, hoping for a cure, or perhaps was one of the family.