"It is an eternal salt-covenant before G‑d." (Num. 18:19)

The words "it is an eternal covenant" mean that the covenant described as a "salt-like covenant" is an eternal covenant. Just as salt preserves the meat indefinitely, so this type of covenant endures indefinitely.

The major ingredient of salt is water. Due to the power of the sun which shines upon it, it turns into salt. In other words, salt represents a fusion of the elements fire and water. Similarly, the covenant is a combination of the attributes Mercy and Justice.

Jacob…even tithed his children….

The share of the Levites is the tithe which in itself is an allusion to the tenth sefira. This is why the Torah phrases this, "To the members of the tribe of Levi: I have given every tithe in Israel as a heritage," etc.

You will find that Jacob treated his son Levi as the tenth amongst his sons. Jacob took the vow to tithe everything G‑d would give him so seriously that he even tithed his children!

When a shepherd wants to tithe every tenth of his flock as prescribed by the Torah, he first leads all the sheep into the fold and then counts them individually, one by one. The last one in, then, becomes the first one out. Similarly, when Jacob, a shepherd, set out to tithe one of his children, he first brought them into the fold commencing with his eldest Reuben and concluding with his youngest Binyamin. When he counted them subsequently, commencing this time with Binyamin, Levi was the tenth and therefore became sanctified.

[Selected with permission from the seven-volume English edition of "The Torah Commentary of Rebbeinu Bachya" by Eliyahu Munk.]