"Pray to your Father in secret"
Jesus says, “When you pray, go into your chamber.” Now, what are these chambers but the heart signified in the Psalm where it is said: “The things you say in your hearts, be sorry for in your room." He then continues: “And closing the doors, pray in secret to our Father.” Our entering the room is not enough if the door is left open to the importunate, for external things enter brazenly in through this door, and lay hold on our interior affections. Temporal and visible penetrate through this door, that is, one of the senses, they enter our thoughts and by a swarm of fancies noisily disturb us while engaged in prayer. Therefore, the door must be closed; that is to say, the bodily sense must be resisted, so that a wholly spiritual prayer may be offered to the Father. For this prayer is formed in the depths of the heart where a man prays in secret to the Father. “And your Father, who sees in secret, will reward you…”
The Lord does not admonish us to pray but teaches us how to pray, just as the preceding passage does not admonish us to give alms but tells us what our intention ought to be when we are giving them. This is due to the fact that he demands the purity of heart that one can only obtain by a continuous and undivided striving for eternal life through no other motive than a pure love of wisdom.