Ye are as graves which appear not - In Matthew 23:27, our Lord tells them that they exactly resembled white-washed tombs: they had no fairness but on the outside: (see the note there) but here he says they are like hidden tombs, graves which were not distinguished by any outward decorations, and were not elevated above the ground, so that those who walked over them did not consider what corruption was within; so they, under the veil of hypocrisy, covered their iniquities, so that those who had any intercourse or connection with them did not perceive what accomplished knaves they had to do with.

(13) Woe unto you, scribes and Pharisees, hypocrites! for ye are as graves which appear not, and the men that walk over [them] are not aware [of them].
(13) Hypocrites deceive men with an outward show.

Woe unto you Scribes and Pharisees, hypocrites,.... As they are all along called by Matthew; though only here by Luke. The Vulgate Latin only reads, "woe unto you", leaving out all the rest: but the whole is retained in all the Oriental versions;
for ye are as graves which appear not; being covered with grass; "or which were not marked", as the Ethiopic version renders it; that is, were not whited or covered with lime, as some were, that they might be seen at a distance, and be known what they were; that so men might avoid going near them, and prevent their being defiled with them; See Gill on Matthew 23:27.
and the men that walk over them
are not aware of them; and so are defiled by them. Christ compares the Pharisees, because of their hypocrisy, and secret iniquity, both to whited sepulchres, and to those that were not: to those that were, because, like them, they looked beautiful without, and righteous in the sight of men, and yet were inwardly full of all manner of pollution and sin; and to those that were not, because they did not appear to be what they were, and men were deceived by them; and under specious pretences to religion and holiness, were by their corrupt doctrines and practices unawares drawn into the commission of sin. Regard may not only be had to graves covered with grass, or not marked with lime, by which they might be known; but also to what the Jews call, , "the grave of the abyss" (z); a grave that is not known no more than if it was in the bottomless pit: so uncleanness by touching a dead body, which a man is not conscious of, is called the uncleanness of the abyss, or an unknown one (a).
(z) Misn Parah. c. 3. sect. 2. Maimon. Hilch. Parah. c. 3. sect. (a) Maimon. in Misn. Nazir, c. 9. sect. 2. & Pesach. c. 7. sect. 7.

appear not, &c.--As one might unconsciously walk over a grave concealed from view, and thus contract ceremonial defilement, so the plausible exterior of the Pharisees kept people from perceiving the pollution they contracted from coming in contact with such corrupt characters. (See Psalm 5:9; Romans 3:13; a different illustration from Matthew 23:27).

For ye are as graves which appear not - Probably in speaking this our Lord fixed his eyes on the scribes. As graves which appear not, being overgrown with grass, so that men are not aware, till they stumble upon them, and either hurt themselves, or at least are defiled by touching them. On another occasion Christ compared them to whited sepulchres, fair without, but foul within; Matthew 23:27.