According to Kabbalah, it is customary to have a copy of Psalm 121 in the delivery room during labor and at the time of birth. These holy passages arouse God’s mercy for an easy birth and delivery.
Another reason given for this custom is that in this way a child’s Jewish education begins at birth. The first images the child is surrounded with are Jewish holy objects. Later, these holy verses are placed within the baby’s crib (in a safe manner), on the doorway to the baby’s bedroom, and on the front door of the home.
A Song of Ascents. I lift my eyes to the mountains – from where will my help come? My help will come from the Lord, Maker of heaven and earth. He will not let your foot falter; your guardian does not slumber. Indeed, the Guardian of Israel neither slumber nor sleeps. The lord is your guardian; the Lord is your protective shade at your right hand. The sun will not harm you by day, nor the moon by night. The lord will guard you from all evil; He will guard your soul. The Lord will guard your going and your coming from now for all time.
(Content courtesy of www.circumcision.net)