en_tn_condensed/jer/31/33.md

I will place my law within them and will write it on their heart

These two phrases have similar meaning and are combined for emphasis. Here "heart" represents "emotions" or "mind." AT: "My law will be part of their thoughts and emotions." (See: rc://en/ta/man/translate/figs-doublet and rc://en/ta/man/translate/figs-metonymy)

from the smallest of them to the greatest

The words “smallest" and "greatest” used together refer to all people.(See:rc://en/ta/man/translate/figs-merism)