The Celtic Trinity Knot, or the Triquetra, is one of the most common of the Celtic knots and dates back hundreds of years. Triquetra is Latin, and means "three-cornered." One of the earliest, Christian manuscripts - The Book of Kells - is filled with Trinity knots.

Celtic culture thought the number three to be lucky and various meanings of the three pointed Trinity have come forward over the centuries, such as: 

The three stages of Womanhood; Maiden, Mother and Crone.
The past, present and future.
The three elements; earth, water and fire.
The mind, body and spirit.
The heart, soul and mind.

Later, the Christians adopted the symbol to represent the Holy Trinity; the Father, the Son and the Holy Spirit.

Modern day use of the trinity knot has seen it being used in Weddings to represent the eternity of Life, and of Love.

Sounds like a perfect symbol for the beginning of your lives together!