He replied, “Because you have so little faith. I tell you the truth, if you have faith as small as a mustard seed, you can say to this mountain, ‘Move from here to there’ and it will move. Nothing will be impossible for you” (Mt 17:20).
St. Thomas Aquinas, the Angelic Doctor of the Church, defines faith as both a theological, infused virtue, which simply cannot be had without the Lord first having freely given it to us. Additionally, faith is an authentically human act of the intellect assenting to divinely revealed truths that comprise the Sacred Deposit of Faith, by command of the Will. Yet, the human will would not move the intellect to assent to these truths without first being inspired or moved by the Spirit of God, which acts on the will. Thus, while it is true to say that every act of faith is simultaneously an act of both God and man, working together, as it were, we must realize that the Lord is the one Who initiates this process. Faith is one of three Theological, infused virtues, the other two being Hope and Charity. It is not possible for human persons to cultivate these virtues from a purely natural standpoint; rather, they begin as free gifts of God, that we are called to cultivate.