Here are some populare "Prayers, Psalms or Poems" used in commitment cerimonies. These are just sample, you can be as original or traditional as you both decide.

SONNET 116 by William Shakespeare
THOUGHTS ON LOVE by Emmet Fox
FIRST CORINTHIANS
TRADITIONAL IRISH BLESSING
LORD’S PRAYER

SONNET 116 by William Shakespeare

Let me not to the marriage of true minds
Admit impediments. Love is not love Which alters when it alteration finds, Or bends with the remover to remove: O no! it is an ever-fixed mark That looks on tempests and is never shaken; It is the star to every wandering bark,
Whose worth's unknown, although his height be taken. Love's not Time's fool, though rosy lips and cheeks Within his bending sickle's compass come: Love alters not with his brief hours and weeks, But bears it out even to the edge of doom. If this be error and upon me proved, I never writ, nor no man ever loved.