Explain why catholic marriage is a sacrament?

im writing a paper about marriage as a sacrament and i just cant put it into words.. ive been researching and researching and i cannot find one single source that tells me straight up why it is a sacrament under Catholic belief. can someone thoroughly explain? (but a little bit straight to the point)
Update: look up "catholic marriage/matrimony as a sacrament" and youll find a million sources on why it is a sacrament.. im catholic and they teach it at school. THATS where i heard it.. and no i do not have the wrong word.
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