This incident followed the preceding one immediately. As Jesus had disappeared ( Luke 24:31), so He now appeared. The doors to the room were shut ( John 20:19). Luke stressed that it was indeed Jesus by writing, "He Himself stood in their midst."[source]
Some translations include the disputed reading "And He said to them, Peace be with you" (e.g, NIV). A scribe who was familiar with John 20:19 may have included this sentence in a later copy of this Gospel. It has strong textual support in John but not in Luke. [source][source][source]