Timothy Keller emphasizes that true understanding of salvation by grace manifests in radical love and joy. He argues that if individuals do not experience significant growth in their ability to love everyone, including their adversaries, it indicates a lack of awareness of their own sinful nature and the grace that redeems them. This growth in love is essential for recognizing one’s need for grace.

Furthermore, Keller highlights the importance of confidence and joy, even amid life's challenges. A lack of these qualities suggests that one may not fully grasp the implications of being saved by grace. Therefore, the presence of humble love and deep-seated joy is a testament to a genuine relationship with God and an acknowledgment of one's sins and the grace that covers them.