An excellent comment from the Rev. Karl Hess posted here was helpful to me lately in answering a student’s question about the Lutheran view of baptism:
“But it would be very bad if we were to baptize people that we knew did not believe. That’s what Luther says in the Church Postil sermon on the gospel for the third Sunday after Trinity:
“…it is a mockery of holy baptism, when they go on and baptize little children, although they teach that they have no faith of their own. They thus sin against the second commandment, in that they consciously and deliberately take the name and Word of God in vain. Nor does the excuse help them which they plead, that children are baptized upon their future faith, when they come to the age of reason. For the faith must be present before or at least in the baptism; otherwise the child will not be delivered from the devil and sins.”
“…if their opinion were correct, all that is done with the child in baptism is necessarily falsehood and mockery. For the baptizer asks whether the child believes, and the answer for the child is: Yes. And he asks whether it desires to be baptized, and the answer for the child is again: Yes, Now nobody is baptized for the child, but it is baptized itself. Therefore it must also believe itself, or the sponsors must speak a falsehood, when for it they say: I believe. Furthermore, the baptizer declares that it is born anew, has forgiveness of sins, is freed from the devil, and as a sign of this he puts on it a white garment, and deals with it in every way as with a new, holy child of God: all of which would necessarily be untrue, if the child had not its own faith. Indeed, it would be better never to baptize a child, than to trifle and juggle with God’s Word and sacrament, as if he were an idol or a fool.”
“…31. If now we cannot give a better answer to this question and prove that the little children themselves believe and have their own faith, my sincere counsel and judgment is, that we abstain altogether and the sooner the better, and never baptize a child, so that we may not mock and blaspheme the adorable majesty of God by such trifling and juggling with nothing in it. Therefore we here conclude and declare that in baptism the children themselves believe and have their own faith, which God effects in them through the sponsors, when in the faith of the Christian church they intercede for them and bring them to baptism.”
The rest of the sermon is here:
Hess sums up:
So, in short, Acts 8 does teach that we ought to baptize those who believe and not those who do not. But simply we cannot know just from a person’s confession of faith that they really believe. It would be mocking God if we baptized people whom we know do not believe. But in the case of babies, whom Christ commands to be brought to Him, and in the case of adults who confess faith in Christ we baptize not on the basis of their faith (as Luther says in the Large Catechism) but on the basis of God’s command, “Go make disciples of all nations, baptizing them in the Name of the Father, and of the Son, and of the Holy Spirit.” But we don’t knowingly baptize those who don’t believe, or surreptitiously snatch babies away from their parents and baptize them secretly.
Here are a couple other posts to look at that deal with this matter of whether or not babies can trust God:
I am persistently puzzled by anyone who insists that they cannot. For in order to enter the kingdom of heaven, one must become like a child.