Pseudo-Chrysostom
Catena Aurea · Matthäusevangelium 6
And when thou prayest, thou shalt not be as the hypocrites are; for they love to pray standing in the synagogues and in the corners of the streets, that they may be seen of men. Verily I say unto you, They have their reward. But thou, when thou prayest, enter into thy closet, and when thou hast shut thy door, pray to thy Father which is in secret; and thy Father which seeth in secret shall reward thee openly.
We may also understand by the door of the chamber, the mouth of the body; so that we should not pray to God with loudness of tone, but with silent heart, for three reasons. First, because God is not to be gained by vehement crying, but by a right conscience, seeing He is a hearer of the heart; secondly, because none but thyself and God should be privy to your secret prayers; thirdly, because if you pray aloud, you hinder any other from praying near you.