The use of the word “buy” suggests that these Christians need to dig into their (spiritual) pockets to find money for the purchase. Given their bankruptcy as described in Revelation 3:17, they have nothing to offer Jesus in payment for his products. In fact, gold is itself a form of currency that one can use to buy something. In a word, Jesus’ products are beyond their reach. Jesus’ own allusion to Isaiah 55:1 infers that Jesus’ products are in fact free: “without money and without price.” The gospel of grace is always free for undeserving sinners.
18 I counsel you to buy from me gold refined by fire, so that you may be rich, and white garments so that you may clothe yourself and the shame of your nakedness may not be seen, and salve to anoint your eyes, so that you may see.