Serving Hashem with all our hearts, means serving Him with tefilla, prayer. "The purpose of tefilla is the elevation of the thinking, feeling, and desiring inner being of Man to a state of being worthy of getting near to God and His benevolence." — Rav Shimshon Raphael Hirsch
Note: This shiur was given as a zechus for Eyal, Naftali and Gilad. The first 15 minutes include a discussion of what it means to daven to Hashem for somebody or something — how do we reconcile accepting God's Will with asking for our own needs and desires?