“I advise you to buy from Me gold refined by fire so that you may become rich, and white garments so that you may clothe yourself, and that the shame of your nakedness will not be revealed; and eye salve to anoint your eyes so that you may see…” (Revelation 3:18-30)
“Lost people have no way to buy salvation (Isaiah 64:5–6). The buying here is the same as the invitation in Isiah 51:1: “Ho! Every one who thirsts, come to the waters; and you who have no money come, buy and eat. Come, buy wine and milk without money and without cost.” All sinners have to offer is their hopelessly lost condition. In exchange, Christ offers His righteousness to those who truly repent.”
-John MacArthur, Because the Time Is Near, 101.