You believe that God is one; you do well. Even the demons believe—and shudder!
James 2:19
"That ye believe on Him" not, that ye believe Him. But if ye believe on Him, ye believe Him; yet he that believes Him does not necessarily believe on Him. For even the devils believed Him, but they did not believe on Him... For, "to him that believeth on Him that justifieth the ungodly, his faith is counted as righteousness." What then is "to believe on Him"? By believing to love Him, by believing to esteem highly, by believing to go into Him and to be incorporated in His members... Not any faith of what kind soever, but "faith that worketh by love." This cannot happen unless hope and love are added.
--St. Augustine
Scripture's axiom in regard to the relationship between faith and love is clear: "faith without love is nothing" (1 Corinthians 13:2); "love believes all things" (1 Corinthians 13:7); and "faith working through love" (Galatians 5:6). Scripture teaches through these and other passages that one must love God in order to truly believe on Him. Loving God for who he is compels the true seeker to believe in him, even though he cannot see him and even though he may be surrounded by circumstances that tempt him to deny God's love and integrity. Unless love of God is the basis of faith in him, the mental effort required to believe firmly is simply too much for the individual mind to sustain. The mental exercise of raw faith, without love, results in a distortion of and revulsion towards the personality of the thing believed.
--Robert Sungenis, Not by Faith Alone, p. 552-553