This concept of love for G-d appears explicitly only once or twice in all the preceding books of Torah, but dominates the chapters of D'varim. Likewise, in the passage above, Moshe speaks of love for G-d, a response that is simple and ultimately fair. We are to love him wholeheartedly because he has first shown his love toward us. But something within our human nature blocks this love for G-d, and must be removed if we are to respond fully. Love for God requires a profound inward change, an inner transformation that Torah describes as the circumcision of the heart.
Circumcision is, of course, a highly significant term.
In the simplest sense it is the removal of a covering or obstacle. Circumcision of the heart is a metaphor for repentance, return to the L-rd. But there is more. Circumcision of an infant boy on the eighth day is called b'rit milah , the covenant of circumcision. This ritual involves far more than the mere medical procedure to remove a fleshly covering.