The last supper was the only event that Jesus asked his followers to annually celebrate:  "The Lord Jesus took a loaf and after thanking God he broke it, saying, 'This means my body broken for you.  Do this in memory of me.'  In the same way he took the cup after supper, saying, 'This cup means the new covenant ratified by my blood; as often as you drink it, do it in memory of me.' "  I Corinthians 11:24, 25  Moffatt Translation

"For we know that since Christ was raised from the dead, He cannot die again; death no longer has mastery over Him.  The death He died, He died to sin once for all, but the life He lives to God."  Rom. 6:9, 10  NIV  This tells us that the remembrance of the Lord's supper celebrates the one and only time Jesus died for the sin of all mankind, guaranteeing their resurrection.

The effects of keeping this memorial of Jesus' death include a closer union with our Lord and a more fervent love and deeper appreciation of God's gift of "His only begotten son, that all who believe in Him should not perish, but have everlasting life."  John 3:16