Knowledge (“notitia”) and agreement (“assensus”) are still not enough to form faith. We need a third ingredient. This third and final ingredient leads a person to move from “believe that” to “believe in.” Reformed theologians called it “fiducia” or “trust and reliance”.  According to “Concise Theology: A Guide to Historic Christian Beliefs,”
Without fiducia there is no faith, but without notitia and assensus there can be no fiducia… [It is] personal dependence on the grace of Father, Son, and Spirit for salvation, with thankful cessation of all attempts to save oneself by establishing one’s own righteousness… 
When we try to work for our salvation, when we try to establish our own righteousness, we are not trusting in God but trusting in ourselves.
According to the apostle Paul, that’s why the Jews did not receive salvation from the Lord.
Brothers, my heart’s desire and prayer to God for them is that they may be saved. For I bear them witness that they have a zeal for God, but not according to knowledge. For, being ignorant of the righteousness of God, and seeking to establish their own, they did not submit to God’s righteousness. (Romans 10:1-3, emphasis added.)
To trust and rely on the Lord Jesus is to submit to Him. “As a result of knowledge about Christ and a conviction that these things are true there must also be a settled trust, a moving of the will—a decision must be made as an act of the will.”  It is to reject reliance upon ourselves and to admit that without the Lord we cannot do anything. It is to rest everything on Him. Somebody wrote, “Faith is an activity which takes men right out of themselves and makes them one with Christ.” This is what Jesus invited us to do.
Come to me, all who labor and are heavy laden, and I will give you rest. Take my yoke upon you, and learn from me, for I am gentle and lowly in heart, and you will find rest for your souls. For my yoke is easy, and my burden is light. (Matthew 11:28–30)
We confess to Christ that we have come to the end of the rope. That we cannot do anything to obtain rest or earn our salvation. We can only receive it from Him. Then we surrender to Him. Then we receive rest for our souls.
 J. I. Packer, Concise Theology: A Guide to Historic Christian Beliefs (Wheaton, IL: Tyndale House, 1993). Electronic edition.
 Paul P. Enns, The Moody Handbook of Theology (Chicago, IL: Moody Press, 1989), 332. Italics his. Italics his. Emphasis added.