What does Jesus mean when he says a person must be "born of water and the Spirit" to enter the kingdom of God? Is he saying that you have to be baptized with water to be counted among God's people?

I think the short answer has to be "Not necessarily, but usually." God can certainly save someone apart from water baptism. But God uses baptism to engage with us and to communicate his grace, so that is the usual practice in the church today.

We do well to keep in mind, though, the example of the criminal who was crucified along with Jesus. This man saw who Jesus was, and he asked to be remembered when Jesus came into his kingdom. And Jesus told him, "Truly I tell you, today you will be with me in paradise" (Luke 23:43).

In John 3, I think Jesus is echoing prophets like Ezekiel, who spoke about water as a symbol of cleansing from sin, and about the Spirit of God, who comes to fill us and renew our hearts (Ezekiel 36:24-27). That symbolism is picked up by John and Jesus in their practice of baptism.

Now this leads to another question: If a person is baptized as a baby or adult, does that mean they are saved? Not necessarily. Some people who are baptized might reject God. But, as some teachers have noted, baptism places us in the community of faith, the church, where we can grow to know and live by God's covenant love and grace.