What is assurance?

From The Whole Christ:

"The Confession of Faith states that rather than produce antinomianism and license, assurance produces gracious fruits. In essence, it involves what the Westminster Divines describe as an enlarged heart:

In peace and joy;
In love and thankfulness;
In strength and cheerfulness in duties. (WCF18.3)

This conforms well to the joyful confidence of the New Testament church. There, assurance of salvation produced boldness in witness; eagerness and intimacy in prayer; poise in character in the face of trial, danger, and opposition; and joy in worship.

The lack of these is also evidence of a lack of assurance that produces them, for rather than breed presumption or antinomianism, assurance produces humility. Christian assurance is not self-assurance and self-confidence. It is the reverse; confidence in our Father, trust in Christ as our Savior, and joy in the Spirit as the Spirit of sonship, seal of grace, and earnest of our inheritance as sons and daughters of God. When these are the hallmarks of our lives, then the grace of our Lord Jesus Christ has come home to us in full measure.

And that, surely is one of the great needs of our times."

The Whole Christ: Legalism, Antinomianism, & Gospel Assurance - Why the Marrow Controversy Still Matters, Sinclair Ferguson, Crossway, 2016, pp. 225-226.

12:06 pm edit for typo. "the grace of our Lord Jesus Christ has come to us" not "to use."