The Seven Sacraments were instituted by Christ, himself, to give Grace to mankind. The term "Sacrament" is best defined as "An outward sign instituted by Christ to give Grace". When we consider the definition, we break it into three parts;
1. "An Outward Sign": Because we are humans, Christ needed material symbols that we humans could attach to, understand and/or perceive. These are the "Things (Water and Oil) and Words or Gestures that we use when conferring a Sacrament.
2. Instituted by Christ: Jesus Christ "Created" the seven Sacraments from when He began His public life, until His death on the Cross. When He Ascended into Heaven, there was an end to the creating of Sacraments. There will always be seven Sacraments... no more, no less. The Church can not institute new Sacraments.
3. To give Grace: Jesus instituted the Sacraments for the essential purpose of conferring God's Grace upon us humans.