Most commentators say it's baptism in water, into the Name of the Father, the Son and the Holy Spirit.
Some commentators say it's baptism in or by the Holy Spirit.
Craig has leaned toward the view that it's the baptism Jesus underwent for us when he died on the cross; that it's Jesus' identification with us. (I'm simplifying here.)
I've leaned toward the view that it's baptism into the Name of the Father, the Son and the Spirit, which has two parts: the part where someone baptizes us with water, and the part where Jesus baptizes us with the Holy Spirit.
I commented there, including a summary...
Whatever interpretation we take, I think we can agree on certain things:
1. Baptism should unite, not divide, true Christians.
2. Baptism is the God-given initiation into life as a believer.
3. There’s a sense in which Jesus is baptized for us, a sense in which Jesus baptizes us in the Spirit, and a sense in which someone baptizes us in water as a sign of new life in God (especially in Jesus).
Do you have any further insights for Craig or for me? (If basically for him, leave it on his blog; if basically for me, leave it on mine. Remember that neither of us will permit you to use our space for bashing sound Christians who don't fully agree with you.)