From Commentary on the Psalms, 36 (390-397)
We must always meditate on God’s wisdom, keeping it in our hearts and on our lips. Your tongue must speak justice, and the law of God must be in your heart. Hence, Scripture tells you: “you shall speak of these commandments when you sit in your house, and when you walk along the way, and when you lie down, and when you get up.” Let us than speak the Lord Jesus, for he is wisdom, he is the word, the Word indeed of God.
It is also written: “open your lips, and let God’s word be heard.” God’s word is uttered by those who repeat Christ’s teaching and meditate on his sayings. Let us always speak this word. When we speak about wisdom, we are speaking of Christ. When we speak about virtue, we are speaking of Christ. When we speak about justice, we are speaking of Christ. When we speak about peace, we are speaking of Christ. When we speak about truth and life and redemption, we are speaking of Christ.
Meditate, then, at all times on the things of God, and speak of the things of God, “when you sit in your house.” By house we can understand the church, or the secret place within us, so that we are to speak within ourselves. Speak with prudence, so as to avoid falling into sin, as by excess of talking. “When you sit in your house,” speak to yourself as if you were a judge. “When you walk along the way,” speak so as never to be idle. You speak “along the way” if you speak in Christ, for Christ is the way. When you walk along the way, speak to yourself, speak to Christ. Hear him say to you: “I desire that in every place people should pray, lifting holy hands without anger or quarreling.” When you lie down, speak so that the sleep of death may not steal upon you. Listen and learn how you are to speak as you lie down: “I will not give sleep to my eyes or slumber to my eyelids until I find a place for the Lord, the dwelling place for the God of Jacob.” And when you get up or rise again, speak of Christ, so as to fulfill what you are commanded.
St. Ambrose (ca. 334-397) became Archbishop of Milan at a time of bitter strife about Christological doctrine, and upheld orthodox teaching in a his widely circulated sermons and treatises. He is credited with introducing hymns to the Western Church, some composed by himself, and his greatest disciple was the even more influential St. Augustine. His commentary on twelve psalms, a collection of earlier sermons, was published near the end of his life. His feast day is December 7.