Why do we need sacraments in the first place?
We need sacraments in order to outgrow our petty human life and to become like Jesus through Jesus: children of God in freedom and glory.
In Baptism the fallen children of men become cherished children of God; through Confirmation the weak become strong, committed Christians; through Penance the guilty are reconciled; through the Eucharist the hungry become bread for others; through Matrimony and Holy Orders individualists become servants of love; through the Anointing of the Sick the despairing become people of confidence. The sacrament in all the sacraments is Christ himself. In him we men, lost in selfishness, grow and mature into the true life that has no end.
Why is faith in Jesus Christ not enough? Why does God give us the sacraments, too?
We can and should come to God with all our senses, not just with the intellect. That is why God gives himself to us in earthly signs especially in bread and wine, the Body and Blood of Christ.
People saw Jesus, heard him, could touch him and thereby experience salvation and healing in body and soul. The sensible signs of the sacraments show this same signature of God, who desires to address the whole man, not just his head. (YOUCAT questions 172-174)