Ever notice that things happen in threes? In fact, even our existence can be broken down into three stages: birth, life, and death. Every moment of our life falls into one of three time periods: past, present, or future. Our very being is a makeup of body, mind, and spirit. Thought, word, and deed complete our human capabilities. There are three kingdoms of matter (animal, plant, and mineral), three primary colors (red, yellow, and blue), three parts to any story (beginning, middle, and end), and three goals in a hat-trick. OK, that last one may be a reach, but all the same, in every instance the number three signifies entirety. The number three points to what is real, essential, and substantial. The number three is perfect completion.
In Scripture, the denotation of the number three as completion is upgraded to Divine completion. When used in Scripture, the number three shares in the perfection of the number seven and epitomizes what is perfect, complete, and divine. The supreme instance of Divine perfection is the Trinity: three persons in one God: God the Father; God the Son; and God the Holy Spirit. In Isaiah 6:3, the Seraphim cry, "Holy, holy, holy." One 'holy' is said in honor of each of the three persons of the Trinity. So too, in Rev 4:8, the living creatures also praise each person of the Holy Trinity by singing, "Holy, holy, holy."
Throughout Scripture, the number three reveals completion in a multitude of examples. In the Old Testament, God's covenant with His people involves three promises: land, dynasty, and world wide blessing. In Exodus 5:3 the Israelites leave the bonds of Egypt by taking a "three days journey into the wilderness." The Ark of the Covenant held the Ten Commandments, a bowl of manna, and Aaron's staff. In Num 6:23-24, three priestly blessings are bestowed upon the Israelites. Solomon's downfall is the result of a tri-fold multitude: wives, gold, and horses, and the list goes on... and on... and on.
In the New Testament, we see the fullness of God's perfect plan in the number three. Mary, the Ark of the New Covenant, holds in her womb the Word made flesh, the Bread of life, and the King of kings. With His three-fold "it is written" response to the devil during the temptation in the desert (Mt 4), Jesus shows that the Word of God is complete perfection. Three times a voice is heard from heaven proclaiming Christ as the Son of God (Mt 3:17, 17:5; Jn 12:28) and each occurrence confirms an aspect of the three fold office of Christ: that of prophet, priest, and king. It is three times that Jesus says to Peter, "Peter, do you love me?" and directs Peter to shepherd his flock. (Jn 21:15-19) Think about it. What is being completed by this action? (The answer might just be three-fold) Then we see the perfect sacrifice, the completion of the covenant, and the totality of salvation as Jesus is crucified at the third hour and on the third day rises from the dead. In Revelation 1:3 a Divine blessing is bestowed upon the reader, the hearer, and the keeper of the prophecy that is written and the list goes on... and on... and on.
The number three symbolizes fullness, completeness, and Divine perfection. The examples of this in Sacred Scripture as well as everyday life are plentiful; and as I look at my three kids, born three years apart, in three consecutive months, each on a date divisible by three, I realize that God has blessed me with the perfect family and that perhaps those three hours of uninterrupted sleep I get each night are just His way of reminding me!