Jamieson, Fausset and Brown on Matthew 6:5

5. And when thou prayest, thou shalt--or, preferably, "when ye pray ye shall."

not be as the hypocrites are: for they love to pray standing in the synagogues and in the corners of the streets--(See on Mt 6:2).

that they may be seen of men. Verily I say unto you, They have, &c.--The standing posture in prayer was the ancient practice, alike in the Jewish and in the early Christian Church. But of course this conspicuous posture opened the way for the ostentatious.