Our Saviour here cautions them against the same thing in prayer, as he had done before in giving alms, viz. hypocrisy and ostentation, doing this duty upon that design, merely to be taken notice of and applauded by men; it was lawful to pray standing in the synagogues, but not to do it merely to be taken notice of by men for devout persons, nor yet to confine themselves to praying in the synagogues. If they chose to pray standing, that they might be more conspicuous, and in the synagogues, because those places were more holy, (as they might dream), or, which seems rather to be here meant, because there most people would see them, for which purpose only they chose corners of streets, as was the old popish custom upon which account they set up crosses at three way leets?, &c., these things were sinful: but to pray standing was usual, Mark 11:25; and to pray in the synagogues and in the temple standing was usual, Luke 18:13. But those who do it merely for vain glory have their reward, and must expect none from God.
Related Commentaries of Matthew 6:5
Matthew 6:5
5 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.