Psalms 50:18

When thou sawest a thief - Rapine, adulteries, and adulterous divines, were common among the Jews in our Lord's time. The Gospels give full proof of this.

When thou sawest a thief - When you have seen or found one who was intending to commit theft, then (instead of rebuking or exposing him) you have been willing to act with him, and to divide the profits. The words "when thou sawest" would seem to imply readiness and willingness to engage with them, as "at first sight." Whenever there was an opportunity to share in the results of theft, they were ready to engage in it. The main "point" in this is, that they were willing to do so even when observing the outward duties of religion, and when professing to be the true worshippers of God. A similar sentiment occurs in Romans 2:21. See the notes at that passage.

Then thou consentedst with him - literally, Thou didst delight in him, or hadst pleasure in him. He was a man after thine own heart. Thou wast at once on good terms with him.

And hast been partaker with adulterers - Margin, as in Hebrew, "thy portion was with adulterers." This was a common vice among the Jewish people. See the notes at Romans 2:22. The idea here is, that they were associated in practice with adulterers; they were guilty of that crime as others were. The point of the remark here is, that they did this under the cloak of piety, and when they were scrupulous and faithful in offering sacrifices, and in performing all the external rites of religion.