If some of the baptized end up in hell, how can baptism be an instrument of assurance?
Might as well ask the same question about the word: If some who hear the Word end up in hell, how can the Word be an instrument of assurance?
In both cases, the answer is: Baptism and the Word failed to assure because those who received the promise did not believe it, or did not continue to believe it. They made God a liar.
The problem occurs when we're looking for some ground of assurance more solid, certain, well-grounded than the promise of God.
But there is no better ground for assurance than the mercy of God.
Baptism is God's promise to me, personally, by name. I know that God has promised Himself to me. I'm just supposed to believe that, rely on it. That's the way of assurance.
If I'm looking for some way to peek over God's shoulder (or my own) and see if He really promised Himself to me, I'm looking for something more solid than the promise of God that I can rely on. If I look for something else, I'm looking for the real God behind the God-who-promises.
But there is no other God. And there is no backdoor entrance to His presence. He faces us in Jesus, the Face of the Father, gives promises, assures us in Word and water of His self-commitment to us. We have only to believe it.
Leithart: Assurance
[HT: Borg Blog: Finding Assurance in Baptism]
