A sacrament is an outward efficacious sign institued by Christ to give grace. Jesus Christ himself is the sacrament, as he gave his life to save mankind. His humanity is the outward sign or the instrument of his Divinity. It is through his humanity that the life of the Trinity comes to us as grace through the sacraments. It is Jesus Christ alone who mediated the sacraments to allow grace to flow to mankind.
“The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament.” (CCC 1601)
Catechism of the Catholic Church about the Sacrament