When the Word comes together with the water, then the baptism is valid even if faith is lacking in the person being baptized. For my faith does not make Baptism what it is; rather faith accepts what Baptism is.
It is not the sacrament but faith in the sacrament that justifies. It justifies not because it is performed but because it is believed.
Mrtin Luther put it this way in one of his sermons: “If you believe that through this water you will be saved, it becomes a fact.”
Also Luther, in his Small Catechism, states that “baptism works forgiveness of sins, rescues from death and the devil, and gives eternal salvation to all who believe this, as the words and promises of God declare”.
Faith in the word of the promise to which baptism conjoins is what justifies. Therefore, baptism is the place of justification; a place where faith meets justification.
The validity of baptism must be destinguished from its efficacy. Whereas its validity does not depend on faith, its efficacy does depend on faith.
Baptism delivers the promise that faith clings to.