Why was Jesus standing when Stephen saw Him in Heaven?

Stephen was in the middle of speaking to the Sanhedrin in regards of their rejection of Jesus as the Messiah.  He told them that they were resisting the Holy Spirit just as their fathers had done before them (Acts 7:51-53).  This is the important part to note, because Israel’s leaders had a chance to repent and hearken to the Holy Spirit and recognize Jesus as the Son of God.  This was why Jesus was standing when Stephen saw Him in the heavens; He was prepared to come back at that point and set up the Millennial Reign.  However, God knew they would reject Him yet again, which they did with the stoning of Stephen (Acts 7:54; 57-59).  Even though God knew they would reject Him again at this point, He still offered them the chance to repent (2 Peter 3:9).  All of this was done so prophecy could be fulfilled and the Gentiles would have a chance for salvation (Matthew 12:18-21).