We can be certain we already possess eternal life
God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. I write these things to you who believe in the name of the Son of God that you may know that you have eternal life. 1 John 5:11-13
Lord Jesus, my assurance of eternal life is built on you and your righteousness, and nothing else, period. I didn’t need a second chance, I needed you to be the second Adam—fulfilling the law for me, and taking the judgement I deserve. I didn’t need to “turn over a new leaf”; I needed to become a new tree. I didn’t need a fresh start; I needed a new heart. I have eternal life right now, only because of God’s free, sovereign, irresistible, more-than-sufficient grace. Even the faith I needed to receive saving-grace, God gave that to me as well (Eph. 2:8-10). Hallelujah!
We can be certain God, who began our salvation, will complete it
And I am certain that God, who began the good work within you, will continue his work until it is finally finished on the day when Christ Jesus returns. Philippians 1:6
Father, my salvation is a work I didn’t begin, and you alone can finish. I could never perform my way out of my sin, or earn my way into your love. From beginning to end, my salvation is 100% all by your grace. I contribute nothing to my salvation but my sin; but you gave me everything I need in your Son. This humbles me, because I am that needy. It gladdens me, because you are that generous. For so great a salvation I worship you. For so great a Savior, I adore you. With so great a hope, I rest in your love, and purpose to live for your glory. In Jesus’ name I pray, Amen.