"Of The Father's Love Begotten" is a beautiful and ancient hymn. Written in Latin in the 5th century by Aurelius Prudentius (translated in the 19th century by Henry W. Baker and J.M. Neale); the tune is Divinum Mysterium, an 11th century chant. You can find a good discussion of this hymn, along with other typically incisive insights here, in an article by the indispensible Anthony Esolen. May you have a Blessed Advent.