Adam Clarke on Exodus 34:21

In earing time and in harvest thou shalt rest - This commandment is worthy of especial note; many break the Sabbath on the pretense of absolute necessity, because, if in harvest time the weather happens to be what is called bad, and the Sabbath day be fair and fine, they judge it perfectly lawful to employ that day in endeavoring to save the fruits of the field, and think that the goodness of the day beyond the preceding, is an indication from Providence that it should be thus employed. But is not the above command pointed directly against this? I have known this law often broken on this pretense, and have never been able to discover a single instance where the persons who acted thus succeeded one whit better than their more conscientious neighbors, who availed themselves of no such favorable circumstances, being determined to keep God's law, even to the prejudice of their secular interests; but no man ever yet ultimately suffered loss by a conscientious attachment to his duty to God. He who is willing and obedient, shall eat the good of the land; but God will ever distinguish those in his providence who respect his commandments.