Why Partake of the LORD's Table

Is the LORD's Table a ceremony of tradition? Why did Christ institute this remembrance? What was the Old Testament Feast of the Passover and how was it made obsolete? Why does the LORD no longer have to Passover His chosen sinners? Why was a 'covering' needed for the sin of chosen sinners up until Christ died Himself? How does the LORD's Table reflect God's dealing in mercy those He chose in His Son before time began? What was the cost of this mercy? What does leaven signify? How is there rest in all that Christ accomplished for His children? Why was work forbidden on the days of rest, what did it typify? Did Christ control what was happening to Him even when He was on the cross? Was Christ made a sinner at any point or did He remain perfect? What are the criteria for those that partake?