Jamieson, Fausset and Brown on Matthew 6:2

2. Therefore, when thou doest thine alms, do not sound a trumpet before thee--The expression is to be taken figuratively for blazoning it. Hence our expression to "trumpet."

as the hypocrites do--This word--of such frequent occurrence in Scripture, signifying primarily "one who acts a part"--denotes one who either pretends to be what he is not (as here), or dissembles what he really is (as in Lu 12:1, 2).

in the synagogues and in the streets--the places of religious and secular resort.

that they may have glory of men. Verily I say unto you--In such august expressions, it is the Lawgiver and Judge Himself that we hear speaking to us.

They have their reward--All they wanted was human applause, and they have it--and with it, all they will ever get.