John Calvin on Jeremiah 34:19

He adds, The princes of Judah and the princes of Jerusalem, etc. He does not here name them as though they were different persons, but he speaks by way of amplifying. He then says that he would punish these chief men, lest they should think themselves to be exempted, because they were superior to others in rank and honor; for we know that those who are elevated in the world are so filled with pride, that they deem themselves as free from all laws. This, then, is the reason why God expressly names the princes and the eunuchs. But he does not mean by the eunuchs those who had been emasculated, as we have stated already in several places. The chief men were called by this name, סרסים serasim. It is rendered “δυνάστας, rulers,” by the Sept., “eunuchs,” by the Vulg. and Syr., and “princes” by the Targ. They were the attendants on royalty, not necessarily eunuchs, for Potiphar, who had a wife, was so called. (Genesis 39:7.) They may have acted as judges; and hence perhaps it is, that they are named here with “the priests.” — Ed

He mentions the princes of Jerusalem, because they were especially proud, on account of their privileges as citizens; for in Jerusalem was the royal residence and the sanctuary of God. But the Prophet declares that their lot would be nothing better than that of the common people, because God would not suffer his holy name to be a mockery and all equity to be violated, and especially the covenant made in his name to be deemed as nothing, and rendered wholly void. At length he names the whole people; whosoever, he says, have passed between the parts of the calf, shall be punished. It follows —

Jeremiah 34:20

20. I will even give them into the hand of their enemies, and into the hand of them that seek their life: and their dead bodies shall be for meat unto the fowls of the heaven, and to the beasts of the earth.

20. Et dabo illos in manum inimicorum ipsorum, et in manum quaerentium animam ipsorum: et erit cadaver ipsorum in cibum avi (hoc est, avibus) coelorum, (est heterosis numeri) et bestiae (hoc est, bestiis) terrae.