Matthew
Matthew 6:6BSB·traditional attribution

But when you pray, go into your inner room, shut your door, and pray to your Father, who is unseen. And your Father, who sees what is done in secret, will reward you.

Matthew Henry Presbyterian @wholebiblehenry

In prayer we have more immediately to do with God than in giving alms, and therefore are yet more concerned to be sincere, which is what we are here directed to. When thou prayest (Mat 6:5). It is taken for granted that all the disciples of Christ pray. As soon as ever Paul was converted, behold he prayeth.

Commenting on Matthew 6:5-8

John Gill Reformed Baptist @doctorgill

But thou, when thou prayest, enter into thy closet,.... Or "chamber", a secret place, fit for private retirement, meditation, and prayer. And when thou hast shut thy door; see some such like phrases in Isa 26:20 where they are used to express security, here secrecy.

Albert Barnes Presbyterian @notesbybarnes

Verse 6. Enter into thy closet. Every Jewish house had a place for secret devotion. The roofs of their houses were flat places for walking, conversation, and meditation, in the cool of the evening. . Over the porch, or entrance of the house, was, however, a small room of the size of the porch, raised a story above the rest of the house, expressly appropriated...