Charles Ellicott Commentary Matthew 6:3

"But when thou doest alms, let not thy left hand know what thy right hand doeth:" — Matthew 6:3 (ASV)

Let not your left hand know — The phrase was probably proverbial, indicating extreme secrecy in the form of a free hyperbole. It is possible that there may be a reference to the practice of using the right hand when offering gifts at the altar.

The symbolic application, though an afterthought, is still suggestive. The “right hand” is the higher spiritual element in us that leads to acts of true charity; the “left” is the baser, self-seeking nature. We ought, as it were, to set a barrier between the two as far as possible—that is, to exclude that mingling of motives, which is at least the beginning of evil.