en_tn/rom/02/29.md

he is a Jew who is one inwardly, and circumcision is that of the heart

These two phrases have similar meanings. The first phrase, "he is a Jew who is one inwardly," explains the second phrase, "circumcision is that of the heart." (See: rc://en/ta/man/jit/figs-parallelism)

inwardly

This refers to the values and motivations of the person whom God has transformed.

of the heart

Here "heart" is a metonym for the inner person. (See: rc://en/ta/man/jit/figs-metonymy)

in the Spirit, not in the letter

Here "letter" is a synecdoche that refers to written Scripture. Alternate translation: "through the work of the Holy Spirit, not because you know the Scriptures" (See: rc://en/ta/man/jit/figs-synecdoche)

in the Spirit

This refers to the internal, spiritual part of a person that the Holy Spirit changes.