True religion requires
1)sacrifice... “Lovest thou me more than these?” -Jesus Christ
2)discipline to Christ, “If ye love me keep my commandments.” -Jesus Christ
3)living correct principles... “Come follow me.” -Jesus Christ
4)and lift up others that cannot help themselves...”If ye have done it unto the least of my brethren than you have done them unto me.” -Jesus Christ
And therein lies the core. If you love Him you do so because of His sacrifice for us. You accept Him as your Savior, knowing you aren't worthy of His grace, but that it's freely given. The sacrifice, discipline and living correct principles are manifestations of the life we come to lead because of our acceptance of Him as our Savior. How can we not do good things knowing what He has done for us?