Albert Barnes Commentary Matthew 23:26

"Thou blind Pharisee, cleanse first the inside of the cup and of the platter, that the outside thereof may become clean also." — Matthew 23:26 (ASV)

Cleanse first, etc. Let them be filled with the fruits of honest industry, and then the outside and the inside will be really clean. By this allusion to the cup and platter, he taught them that it was necessary to cleanse the heart first, that the external conduct might be really pure and holy.