Musar zu Malachi 2:17

And the fifth is that evil speech brings one involved with it to put his mouth to speaking wrongly about God - and as it is stated (Psalms 73:9), “They set their mouths against Heaven, and their tongues range over the earth.” And there is none among all of the sins the punishment for which reaches the punishment for flinging [accusations at God]. And our Rabbis said (Arakhin 15a), “Our ancestors tried the Holy One, Blessed be He with ten trials, but their sentence was sealed only due to the evil speech.” For it is stated (Numbers 14:28), “I will do to you just as you have urged Me, etc.”; and it is stated (Deuteronomy 1:34), “When the Lord heard your loud complaint, He was angry; and He vowed”; and it is stated (Malachi 2:17), “You have wearied the Lord with your talk.” And King David, peace be upon him, said (Psalms 50:16-20), “And to the wicked, God said, ‘Who are you to recite My laws, and mouth the terms of My covenant. [...] When you see a thief, you fall in with him, etc. You devote your mouth to evil, and yoke your tongue to deceit. You are busy maligning your brother.’“ Behold you have learned from this that Torah [study] does not protect those involved with evil speech or one accustomed to steal or to engage in forbidden sexual relations; and that they are not fit to be involved with Torah. And our Rabbis, may their memory be blessed, said (Sotah 21a) [that] because Doeg spoke evil speech, his wisdom did not stand him in. And that which our Rabbis, may their memory be blessed, said - “Sin extinguishes a commandment, but sin does not extinguish Torah, as it is stated (Proverbs 6:23), ‘For the commandment is a lamp, and the Torah is a light’” - they said about someone who sins by chance, and not about one who removes the yoke of the warning of a sin from upon him.

And it is stated in Sifrei, and also in Arachin 15a that our forefathers tried the L-rd ten times, and their decree was sealed only for the sin of lashon hara alone, as it is written (Bamidbar 14:22): "And they tried Me this ten times, and they did not heed My voice," and (Malachi 2:17): "You have wearied the L-rd with your words."