From an outline for a sermon for the Purification of Mary from 1882. Good stuff.
So there you have, my dear ones, the answer, what is the basis of the assurance of a blessed departure from this world and a joyful going home to the eternal heavenly fatherland, namely that we
1. view Christ with Simeon’s eyes of faith, i.e. recognize Him from His Word and Gospel as the eternal, almighty Son of God, Whom the Father in heaven has thrown in and sent, that He enters in our place, pays for all our debt of sin, makes perfect satisfaction with His righteousness, as He has already done under the Law at His circumcision and at His presentation in the temple, so that He fulfills the Law in our place with His active and passive obedience, and finally accomplishes the great work of redemption on the cross.
2. that we hold Him with Simeon’s arms of faith, i.e. devote Christ to ourselves with all His merit in confident trust. For that’s the main thing with faith. If you lack the trust that He has gifted and given you from the Father, that He is your Savior, then you lack everything. But if God gives you the grace that you can believe that even your sin in paid, your guilt is taken away, your punishment is atoned for, that the heavenly Father no longer looks at you as cursed in Adam, but as righteous in Christ, and already received you for the sake of His dear Son by baptism into His covenant of grace as His dear child, then you can joyfully sing: “Thank God! My Jesus cleanses me/From all sins I committed” etc.
So our assurance of a blessed farewell from this world is based on faith alone.
 KELG 63:1