In chapter three of the second book of his treatise On the Holy Spirit, St. Ambrose continues to establish that titles given to the Father and/or the Son are also given to the Holy Spirit:
Let them say, then, wherein they think that there is an unlikeness in the divine operation. Since as to know the Father and the Son is life, as the Lord Himself declared, saying: ‘This is life eternal to know Thee the only true God, and Jesus Christ, Whom Thou hast sent’ (John 17:3), so, too, to know the Holy Spirit is life. For the Lord said: ‘If ye love Me, keep My commandments, and I will ask the Father and He shall give you another Paraclete, that He may abide with you for ever, even the Spirit of Truth, Whom the world cannot receive, because it seeth Him not, neither knoweth Him, but ye know Him, for He is with you, and in you’ (John 17:14,15).
Since we are on the verge of celebrating Christmas and I have spent very little time meditating upon the Nativity, let me try to tie this title Life to the birth of our Lord, God and Savior. During the Vespers of the Nativity, Orthodox Christians sing this Troparion (hymn) of the Prophacies antiphonally between OT readings:
You have dawned from a Virgin, O Christ, You noetic Sun of Righteousness. And a star pointed to You, the Uncontainable, contained within a cave. You have led the Magi to worship You, together with them we magnify You: O Giver of Life, glory be to You.
Thus, the eternal life that we may obtain through our knowledge of God and Jesus Christ is accomplished through the Son becoming a human being. This is further described in the Stichera of Vespers:
Come, let us rejoice in the Lord as we declare this present mystery. The middle wall of partition is broken asunder; the flaming sword is turned back, the Cherubim withdraw from the Tree of Life, and I partake of the Paradise of Delight, whence I was cast out before through disobedience.
Christ Himself, therefore, is called the Tree of Life. Eternal life is granted by our partaking of the Tree once guarded by the Cherubim with their flaming swords (Gen. 3:24). This phrase, however, has many layers in the same way the Orthodox Christian’s answer to the question, “Are you saved?” has many layers:
I am already saved (Rom. 8:24, Eph. 2:5–8), I’m also being saved (1 Cor. 1:18, 2 Cor. 2:15, Phil. 2:12), and I have the hope that I will be saved (Rom. 5:9–10, 1 Cor. 3:12–15).
We partake of Christ the Tree of life because He has taken on our humanity. We also partake of Christ the Tree of Life every time we take communion. In the hymnody of the Orthodox Church the Tree of Life is equated with the Cross. This is done as we pray during the Ninth Hour of the Royal Hours of Christmas:
Master, Lord Jesus Christ, our God, who have long endured our transgressions, and brought us to this hour in which hanging on the life-giving tree you showed the good Thief the way into Paradise and destroyed death by death, have mercy also on us sinners and your unworthy servants.
Thus, though we have partaken of the Tree of Life through the Nativity and we are partaking of the Tree of Life through communion, ultimately we will partake by being crucified with the Tree of Life. Amen.