Charles H. Spurgeon on Psalms 106:33

Because they provoked his spirit, so that he spake unadvisedly with his lips. Which seems a small sin compared with that of others, but then it was the sin of Moses, the Lord's chosen servant, who had seen and known so much of the Lord, and therefore it could not be passed by. He did not speak blasphemously, or falsely, but only hastily and without care; but this is a serious fault in a lawgiver, and especially in one who speaks for God. This passage is to our mind one of the most terrible in the Bible. Truly we serve a jealous God. Yet he is not a hard master, or austere; we must not think so, but we must then rather be jealous of ourselves, and watch that we live the more carefully, and speak the more advisedly, because we serve such a Lord. We ought also to be very careful how we treat the ministers of the gospel, lest by provoking their spirit we should drive them into any unseemly behaviour which should bring upon them the chastisement of the Lord. Little do a murmuring, quarrelsome people dream of the perils in which they involve their pastors by their untoward behaviour.