In Suratur Rum, 30:21, Allah says: “…And among His signs is that He creates for you mates of your kind and causes love and tenderness between you, so you find peace in each other, Indeed in this is a message for people who reflect…” In essence therefore it is a tri-lateral contract between a man and a woman inviting Allah as the third entity.
Man and woman are drawn towards each other because individually we are programmed to feel incomplete. Prophet Adam (pbuh) when created was the ‘richest’ man in all aspects yet sensed a feeling of being incomplete which he could not resolve or understand. It was only when Allah created Sayyida Hawwa that he felt complete. Without the sanctity of Nikah however, man and woman are like two fires which consume each other. Two people may love and care for each other but without inviting Allah into the relationship what is there to bind temporal human beings eternally?
In essence we have two strangers with different personalities and backgrounds going through many different transitions in their lives including the inherent physiological, psychological and emotional differences between man and woman.
Nikah therefore is a commitment of man and woman to the Creator.