I delight to do thy will, O my God: yea, thy law is within my heart. Psalms 40:8

When Satan rebelled in heaven he brought to the attention of the angels, the thought of a law. 
Before that the angels didn't even think about "a law". The angels delighted to do God’s will. They loved God and reigned in heaven in peace and harmony without the thought 
of “oh I must do this and I must not do that”. 
A third of the angels developed iniquity in their 
hearts along with Satan the deceiver and they were removed 
from heaven. 

David, as he writes here in Psalms, sings about how he delights to do God's will for it is natural, imbedded and simply a part of him.

We have to come to a place in our walk when we don’t and won’t have to even give it a second thought to do God’s will for if we truly love Him we will automatically live
for Him and by Him in complete obedience. (John 14:15)

There are many rewards in living for Christ. (Psalms 19:11; Rev. 22:14) Let us pray for
ourselves and others that we might grow to delight to do His will.