Jesus really died. Jesus really rose. These realities are the core of our Faith. This man Jesus, who said and proved that He truly is God blessed, broke and shared bread which He changed into His Body and then He commanded His apostles to do that action in memory of Him. The apostles and by extension the apostolic Church has thus continued our Lord's command which is the core of the Mass. From that core the Mass has developed and is the source and summit as well as the greatest treasure of our Faith.