The Lord will circumcise thine heart; "when thou wilt become better, God will help thereto (cf. Deuteronomy 10:16)" (Herxheimer). When Israel should return to the Lord, he would take away from them the evil heart of unbelief, and give them the new heart and the right spirit. "Qui pravis affectibus renunciat is circumcisus corde dicitur" (Rosenmüller. Cf. Jeremiah 31:33; Jeremiah 32:39; Ezekiel 11:19, etc.; Ezekiel 36:26; Romans 2:29; Colossians 2:11).
Thou shalt return and obey; i.e. thou shalt again hearken (see Deuteronomy 30:9, where the same expression is thus rendered). These two verses are closely connected, the former expressing the condition on which the aspect expressed in the latter depends. They should be rendered accordingly, If thou shalt return … then the Lord thy God, etc. (comp. Genesis 42:38; Exodus 4:23, where a similar construction occurs).