Service to God adds nothing to Him, and He has no need of human obedience. On the contrary, He grants life, incorruptibility and eternal glory to those who follow and serve Him. He bestows benefits on those who serve Him just because they serve Him and on His followers just because they follow Him, but He does not receive any benefit from them because He is rich, perfect, and in need of nothing. God demands service from us not because He needs it but because He is good and merciful and wants to benefit those who continue in His service.
St. Irenaeus of Lyons, Against Heresies IV.14.i
Locus Communis 