Christians began to meet on Sunday because Jesus the Nazarene rose from the dead on the first day of the week.  We give the first day to the One who is the “first fruits from the dead.”  Early Christians met together on the first day of the week (Acts 20:7, I Corinthians 16:2).  John called it the Lord’s Day (Revelation 1:10).  It was the great day when the Lord triumphed over death.  Every first day of the week is a celebration of the resurrection, because the once dead Messiah now lives!

“Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you.” John 20:19 (KJV)