Why do some churches baptize babies?

To start with why we baptize at all, we do it because Jesus has told us to “make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit” Matthew 28:19 (ESV). The Bible teaches that Baptism is a way that God delivers His gifts of grace through the Holy Spirit. In Acts 2:38-39 (ESV), we’re told that the gifts of baptism are for “you and your children.” Jesus blessed children and told us to receive faith as children.

When we read in Ephesians 2:8 (ESV) that “we have been saved through faith. And this is not your own doing; it is the gift of God,” we see our inability to do anything to work for our salvation. So, we baptize babies, not because they can work for their salvation, but because they can’t.

If someone can understand Baptism, should they be taught about it before they’re baptized?

In Acts 8:26-39, we read about an Ethiopian who is seeking to understand the scriptures. Whenever the Bible is read, the Holy Spirit is working. In the case of the Ethiopian, Philip shared the Gospel of Jesus Christ with him and connected what the Ethiopian already knew from reading scripture and worshiping in the temple. After this exchange, the Ethiopian desired to be baptized. In Acts 16:25-33, a jailer is instructed before being baptized. Many churches follow a version of this practice by having formal classes with a group of adults before baptizing them, or a pastor may have more informal visits with an individual in their home. Whether in a church building or at home, with a group or one-on-one, God works through His Word, creating and sustaining faith and fulfilling His promises.