Pseudo-Chrysostom
Catena Aurea · Matthäusevangelium 6
Therefore when thou doest thine alms, do not sound a trumpet before thee, as the hypocrites do in the synagogues and in the streets, that they may have glory of men. Verily I say unto you, They have their reward. But when thou doest alms, let not thy left hand know what thy right hand doeth: That thine alms may be in secret: and thy Father which seeth in secret Himself shall reward thee openly.
The Apostles in the book of the Constitutions, interpret thus; The right hand is the Christian people which is at Christ’s right hand; the left hand is all the people who are on His left hand. He means then, that when a Christian does alms, the unbeliever should not see it.