To my understanding, consecration is a type of devotion, usually consisting of taking a personal vow between yourself and God. A consecration to Jesus through Mary, then, would be a devotion to Mary, and through Mary, bring yourself closer to Jesus. A devotion to Mary, or any Saint, is using them as a sort of role model to better yourself and your relationship with Christ. Like having a mom or dad being a role model for the son or daughter’s relationships with others, such as a romantic relationship.