Besides being rooted in the promises of God in Scripture, assurance of salvation is declared to be the work of God's Holy Spirit. When a person accepts Christ as Savior, he or she is born again. With the new birth, God's Holy Spirit comes to indwell or live in that person. At the same time, John teaches that the Holy Spirit also creates desires in the believer that bring assurance of salvation. Assurance of salvation is the work of the Spirit of God.
Assurance is a product of saving faith.
In Paul's statement of assurance, he cites his own faith. His assurance was vitally linked to believing. It was a product of Paul's saving faith. In seventeenth century England, the revered Puritan divine Thomas Watson described how assurance was produced in an interaction of God's Word, man's conscience and the Holy Spirit's witness. Such interaction in the form of a syllogism results in assurance of salvation for the believer.