Chasidut zu Ejchah 1:16

Exodus 35,1. “these are the things that the Lord ‎commanded to be done. For six days work shall be ‎performed, etc.” Our sages in Shabbat 70 see in the ‎numerical value of the letters in the word: ‎אלה‎ i.e. 39, an allusion ‎to the 39 categories of “work” prohibited to be performed by ‎Israelites on the Sabbath. These categories of work are understood ‎as especially mundane in nature, the Ari z’al pointing out ‎that when the prophet Jeremiah (Lamentations 1,16) says: ‎על אלה ‏אני בוכיה‎, “on account of these things I weep,” he meant that ‎violation of these prohibited activities of the Sabbath require the ‎Jewish people to collectively rehabilitate themselves by a special ‎activity, ‎מלאכה‎, and this is why the positive instruction ‎לעשות‎, ‎‎“to perform,” [and not as “to desist from” Ed.] has ‎been added.‎