Here's a quote I like. It's about baptism and is in the context of discussing the necessity of church membership as identified by the Word (response to the gospel) and the sacraments (sealed in baptism, celebrated etc. in the Lord's Supper).
‘The question is not where our names are written, but where his name is written. In baptism we are numbered among the children of God, receiving the name of our Father, written, as it were, on our foreheads (Mt. 28:19; Rev. 14:1). To be sure, the washing of God’s regenerating grace is accomplished by the water of the Spirit, not that of the font, but the outward sign functions precisely because it is outward; it is the Lord’s visible seal of his invisible grace.’ [italics original]
What a great way of thinking about baptism - our Father's name written forever on our foreheads signifying and sealing the relationship we have with him by grace.
All of which means getting baptised is a little like getting a tattoo!
Or maybe more like getting your marriage certificate?