And this is how I understand it: "Let your light so shine before men, that they may see your good works, and glorify your Father Which is in Heaven" (Mt. 5:16). Let people see your good works, and through this praise the Lord, and have a living example for themselves, a living motivation to do good. This is who you have to hide your good deeds from! [Batiushka pointed to his own heart]. Conceal everything from it; "let not thy left hand know what thy right hand doeth" (Mt. 6:3). The 'left hand' here means your conceit and vanity.

St. John of Kronstadt
From the book: Conversations of Archpriest John of Kronstadt with Abbess Taisia, Sretensky Monastery, 2022