The Heidelberg Catechism asks in question 69:
How does holy baptism signify and seal to you that the one sacrifice of Christ on the cross benefits you?
Answer: In this way: Christ instituted this outward washing and with it gave the promise that, as surely as water washes away the dirt from the body, so certainly His blood and Spirit wash away the impurity of my soul, that is, all my sins.
 Matt. 28:19.  Matt. 3:11; Mark 16:16; John 1:33; Acts 2:38; Rom. 6:3, 4; I Pet. 3:21.
The significance of this sign is the assuredly that the promises made by Christ in salvation will be assured to be accomplished in the life of the believer. But what does that mean? Can a baby understand that, and how does that help the believer later in life?
Theology Simply Profound is a podcast of Westminster Presbyterian Church, an Orthodox Presbyterian Church, serving the western suburbs of Chicago, where God powerfully speaks through his means of grace. Also, check out the work of the OPC in Chicagoland at Chicago Reformed.
Music credit: pamelayork.com. Thank you, Pamela York, for the use of your beautiful jazzy rendition of “A Mighty Fortress Is Our God.” We encourage our listeners to check out her website and consider purchasing some of her music.