Baptism is a particular mark of the start of our Christian life. As such it is first and foremost a sign of the journey which expresses our hope and faith on God, and whilst we have no clear idea of what that life will be for us, we celebrate this mark and the sure promise that Christ is with us till the close of the age.
For many Baptism happens as we are infants, and for some it happens as adults. Clearly the role for sponsors and Godparents will have a different character, however the sacramental call of baptism to shane as a light in the world to the glory of God the Father remains the same.
Baptism is a once sacrament and we do not re-baptise people who have been validly baptised in another denomination, as that would be a breach of our faith in One God, One Church and One Baptism, which is part of our central belief.