Isaiah 43.1-2, Luke 3.15-17, 21-22, Acts 8.14-17
Unlike our other lectionary readings, the beginning of Isaiah chapter 43 is not a passage that is directly about baptism, but it is redolent with themes that are linked to baptism. It talks about the idea that we belong to God, and are called by name to be part of his people. It talks about the idea that God redeems, or sets us free, from all that would hold us captive or enthralled and which would prevent us from realising our true potential. And it talks about us passing through rivers without being overwhelmed and fires without being scorched or consumed. This part of the passage has, perhaps, less to do with baptism and more to do with God being with us in times of hardship, suffering and adventure. But, of course, the mention of waters and rivers immediately conjures up baptismal imagery. And fire and flame might remind us of the Holy Spirit.
More significantly, perhaps, the image of passing through deep waters is often associated in the Bible with dying and reminds us, also, therefore that baptism is a rite of passage. That is to say, it marks an important transition, or staging post, from one state of being to another. For a long time, when people commonly believed that God could only forgive our sins once in a lifetime, they delayed their baptism until they were at the point of death, as the Emperor Constantine did. But there was another ancient tradition, which eventually gained greater popularity, that Christians should baptise their children as soon as possible after their birth, perhaps because life expectancy for infants was once so uncertain. So, either way, baptism soon came to mark a vital moment in a Christian's physical existence - either the point of our entry into life or the point of our leave taking from it.