The confidence we have in God’s work of salvation is firmly established in God. The first — of three — Scripture truths establishing the assurance of our salvation is …
The Father’s Promise — Titus 1:2
1 Paul, a servant of God and an apostle of Jesus Christ for the faith of God’s elect and the knowledge of the truth that leads to godliness– 2 a faith and knowledge resting on the hope of eternal life, which God, who does not lie, promised before the beginning of time, 3 and at his appointed season he brought his word to light through the preaching entrusted to me by the command of God our Savior, … Titus 1:1-3 (NIV)
God promised us eternal life! God is a promise-keeping God who does not lie, and eternal life is how long? FOREVER! Can’t be eternal life if once you’ve received it you can then lose it!