The fact that Christ sacrificed Himself on the cross does not mean that there are no sacrifices for us.  As Christ sacrificed Himself fully we too are to sacrifice ourselves fully to God.  There is no worship without sacrifice.  “Present your bodies a living and holy sacrifice, acceptable to God, which is your spiritual service of worship” (Rom 12:1b).  This worship is more than songs of praise. Singing praise without the sacrifice of a surrendered heart is hypocrisy.

“This people honors me with their lips, but their hearts are far from me.” Matthew 15:8 (NRSV)