Faith.

Geerhardus Vos has written:

“Hence also faith is not a quantitative matter, as it would have to be, were it a principle of human endeavor; faith like a grain of mustard seed will accomplish the greatest conceivable results, because, small though it be, it nevertheless, provided it be genuine faith, connects man with the exhaustless reservoir of divine omnipotence, Lk. xvii. 6.”

(Vos, Geerhardus, The Teaching of Jesus Concerning the Kingdom of God and the Church, Wipf and Stock Publishers, Eugene, Or., 1998, p. 181.)

“In its ultimate analysis faith is, according to Jesus, a divine gift. Faith must be the work of God in man, because only so can it be in harmony with itself as the recognition that we owe everything to God’s working for us and in us.”

(Vos, Geerhardus, The Teaching of Jesus Concerning the Kingdom of God and the Church, Wipf and Stock Publishers, Eugene, Or., 1998, pp. 187-188.)