The fourth act of faith.

Herman Witsius has written:

“Hence arises a fourth act of faith, a hunger and thirst after Christ. For the believing soul knowing, acknowledging and loving the truths of salvation, cannot but wish that all those things which are true in Christ may also be true to him, and that he may be sanctified and blessed in and by those truths: And he seriously desires, that having been alienated from the life of God through sin, he may be again sealed unto the glory of God by free justification, and in that by sanctification. This is that hunger and thirst after righteousness mentioned Mat. v. 6. And pray what reason can be given why he who believes and feels himself a most miserable creature, and is fully persuaded that he can be delivered from his misery by nothing either in heaven or on earth; who sees, at the same time, the fullness of that salvation which is in Christ; and is assured he can never obtain salvation unless he be united to Christ; who from his very soul loves that truth that treats of the fullness of salvation which is in Christ alone, and in communion with him; how is it possible, I say, that such a person would not seriously and ardently desire to have Christ dwelling in him, seek and pant after this, and indeed with such longings, as nothing short of the possession of the thing desired can satisfy: as hunger and thirst are only allayed by meat and drink.”

(Witsius, Herman. The Economy of the Covenants Between God and Man, Volume I, Kingsburg, CA: den Dulk Christian Foundation, 1990, p. 381-382)