"Offer God a sacrifice of praise and fulfill you vows to the Most High." If you praise God you offer your vow and fulfill the promise you have made. So the Samaritan leper, healed by the Lord’s word of command, gained greater credit than the other nine; he alone returned to Christ, praising God and giving thanks. Jesus said of him: "There was no one to come back and thank God except this foreigner." He tells him: "Stand up and go on your way, for your faith has made you whole."
The Lord Jesus, in his divine wisdom, taught you about the goodness of the Father, who knows how to give good things, so that you might ask for the things that are good from Goodness itself. He urges you to pray earnestly and frequently, not offering long and wearisome prayers, but praying often, and with perseverance. Lengthy prayers are usually filled with empty words, while neglect of prayer results in indifference to prayer.
Again, Christ urges you, when you ask forgiveness for yourself, to be especially generous to others, so that you actions may commend your prayer. The Apostle, too, teaches you how to pray; you must avoid anger and contentiousness, so that your prayer may be serene and wholesome.
He tells you also that every place is a place of prayer, though our Savior says: "Go into your room." But by “room” you must understand, not a room enclosed by walls that imprison your body, but the room that is within you, the room where you hide your thoughts, where you keep your affections. This room of prayer is always with you, wherever you are, and it is always a secret room, where only God can see you.
You are told to pray especially for the people, that is, for the whole body, for all its members, the family of your mother the Church; the badge of membership in this body is love for each other. If you pray only for yourself, you pray for yourself alone. If each one prays for himself, he received less from God’s goodness than the one who prays on behalf of others. But as it is, because each prays for all, all are in fact praying for each one.
To conclude, if you pray only for yourself, you will be praying, as we said, for yourself alone. But if you pray for all, all will pray for you, for you are included in all. In this way there is a great recompense; through the prayers of each individual, the intercession of the whole people is gained for each individual. There is here no pride, but an increase of humility and a richer harvest from prayer.
Pray especially for the whole body of the Church
From a treatise on Cain and Abel by Saint Ambrose
The Liturgy of the Hours, Vol. IV, Office of Readings
Monday of the 27th Week of Ordinary Time