You may not realise it, but we are always serving. Serving our mind, our body our boss, our society our family, the laws of our country, our government by paying tax. Everything we do is in service.
So serving God, should come very naturally. As the third step in bhakti yoga, after acquiring faith and the association of devotees, one can be introduced to devotional service. When we come before god, often we ask God for material benefits "Dear God please let me pass this exam, please let me w