Among the various themes in the poetic prophecies of Yirmiya, a particularly prevalent theme in Chapters 34—35 is the power of speech and the requirement to fulfill one’s promises. In Chapter 34, Yirmaya tells Bnei Yisrael that they will face the wrath of Hashem for one particular sin; the failure to maintain the vow that Tzidkiyah the king had made which had granted rightful freedom of the slaves of the people. In stark contrast, perek 35 details the inspiring salvation and protection of the Rechavite family, for the sole reason that they upheld the promises that Yonadav their ancestor had required them to make.
In order to understand the importance of speech, we can examine the Torah. In Parshas Vayetzei, we find the first instance of one being bound by a promise. Yaakov Avinu made a promise to Hashem that if he returned in peace from the house of Lavan, then he would tithe all of his produce to Hashem and would build a Mikdash to Hashem at the place of his prophecy.
According to the Ramban the word neder (vow) is a shortening of the phrase ‘dirah leHashem – a house for G-d’. Thus, the purpose of a vow and the fulfillment of a vow are to bring oneself closer to G-d and to bring Hashem closer to oneself, so to speak. Consequently, we can now comprehend the potency of Yaakov’s neder, since the promise itself was to build a House for Hashem in this world.
The Gemara in Nedarim (22a) states the opinion of Rav Nassan that one who makes a vow is as if he has built an altar, and one who fulfills the vow is considered to have brought an offering to Hashem. The Ran interprets this statement to have two meanings. If one makes a vow which is not L’shem Shamayim, it is as if he has built an altar outside the Temple, which is forbidden. Furthermore, the fulfillment of such a vow would be enough to obligate one to bring a sin offering to Hashem for the metaphorical offering up of a korban on a forbidden altar. However, one whose vows are L’shem Shamayim is considered to have brought a korban in the Beis Haimkdash itself.
The passuk in Vayikra, 2:1, writes “vnefesh ki takriv – when a person offers up”. The word “nefesh” means soul and is therefore a strange word to use in the description of a person. Rashi interprets this to explain that when someone offers up a voluntary korban when his means are scarce, Hashem considers as if he has offered up his very soul. In this light, vows, that are considered to be like korbanos, reflect the manifestation of a person’s desire to come close to Hashem and to sacrifice part of himself to Hashem.
This beautiful idea is illustrated magnificently in Yirmiya Chapter 35 as Hashem instructs the prophet to take the descendants of Yonadav the Rechavite into the Beis Hamikdash itself and to praise them for the fulfillment of their promises. The Rechavites were shown that in Hashem’s eyes, the implementation of one’s promises is comparable to offering up a korban in the Beis Hamikdash. In stark contrast, the destruction of Tzidkiyahu’s kingdom was triggered by their rejection of their promises. It is therefore fitting that the Beis Hamikdash, the paradigm of closeness to Hashem, should be destroyed by failed promises that are reflected by improper korbanos.