For example, the love of God is spoken of as a source of the spiritual life. "You shall love the LORD your God with all your heart" (Deut. 6:5): "And the LORD will circumcise your heart and the heart of your descendants that you may love Him with your entire heart" (Deut. 30:6). "He who loves Me will keep My word" (John 14:23). "Love for God has been poured out in our hearts by the Holy Spirit (Rom. 5:5). "The goal of the commandment is love from a pure heart, a good conscience and a sincere faith" (1 Tim. 1:5). Though the concept is sprinkled in texts throughout the Word of God, the apostle John in his first epistle presses home splendidly the idea that love for God is at the heart of the spiritual life.
Reason and experience affirm the same thing. Whenever a person reflects on his inner motivations, he feels that all is actions and even his affections are motivated by a particular desire that directs and dominates all other feelings. Is this desire and motivating influence anything other than love, the desire that each one has for whatever he considers to be good? So it is with love for God in the case of a Christian. If all our activities and affections must be regulated by the law of God, we must have within us a source principle in keeping with such affections and activities. This must be love for God. If every action of the spiritual life has glorifying God as its highest goal, how can this goal be reached except in a mind where there is a sincere affection for God and an ardent desire to glorify Him? It is precisely this desire that we call love for God. . ." pg.16,17 'The Spiritual Life' by Campegius Vitringa