Jesus is pictured as "sitting" at the right hand of God, rather than standing, in most of the New Testament. But Stephen saw Jesus "standing" in Acts 7:55. Then in verse 58 they cast him out of the city and stoned him to death. Did he break a law or were they mad because Stephen was insinuating the fulfillment of a particular prophecy?
The Son of Man was standing because the throne was already occupied.
In the apocalyptic belief of the time, the Son of Man was God’s divine agent who would one day bring judgment on God’s enemies and inaugurate God’s reign on earth. The clearest picture of the role of the Son of Man in canonical scripture is in Daniel 7:13-14:
“In my vision at night I looked, and there before me was one like a son of man, coming with the clouds of heaven. He approached the [enthroned] Ancient of Days and was led into his presence. He was given authority, glory and sovereign power; all nations and peoples of every language worshiped him. His dominion is an everlasting dominion that will not pass away, and his kingdom is one that will never be destroyed.”
In his speech in Acts 7 describing the failure of the Jewish religious system to understand God’s purpose, Stephen quoted Isaiah 66 wherein God declares, “Heaven is My throne and the earth is My footstool. What kind of house will you build for me?” (v.49). God is not contained in temples, Stephen said, but He rules over heaven and earth, recalling the iconic picture of the seated monarch on the throne of heaven with his feet, his authority, on the earth.
Stephen then added, “Behold, I see the heavens opened up and the Son of Man standing at the right hand of God.” Stephen was declaring that Daniel’s apocalyptic vision was being fulfilled, that the Ancient of Days, seated on his throne, was even now handing authority over to the Son of Man standing at his right hand. The everlasting dominion of the Son of Man had begun! According to the writer of Acts, the Jewish crowd did not embrace this message, and Stephen became the early Christian movement’s first martyr.
In the following centuries Christians came to interpret the Jewish apocalyptic vision differently. As their theology of the divinity of Christ developed, Christians came to think of Daniel’s ‘Son of Man’ and the ‘Ancient of Days’ as the same person: the Son of Man was God’s own son, even God himself, and they sat enthroned over the Kingdom of Heaven and Earth as one person. In Christian doctrine this came to be called the 'Session of Christ', the ‘sitting’ of Christ. In this light Stephen’s vision was reinterpreted, and various explanations have been offered for why Christ was standing rather than seating.
But originally, Stephen saw the Son of Man standing beside the throne, and sitting upon it, according to Daniel 7:9-10, was the Ancient of Days.
To be "seated at the right hand of a king's throne" (see Luke 22:69; Ephesians 1:20; and Colssians 3:1) is to participate and share in the prerogatives of a potentate in the exercise of his authority and power.
Jesus earned the right (so to speak) to be seated at the Father's right hand by dint of having completed the work his Father gave him to do; namely, accomplishing the work of atonement on the cross. His being seated speaks of having finished the task his Father gave him to do.
When Jesus came to earth the first time, he did so by emptying himself of his divine rights and prerogatives and becoming, for a time, a servant (Philippians 2). In his self-emptying he did not by any means cease being God the Son, however. While he chose to do only those things which pleased the Father, his Father allowed him to accomplish many miracles, including raising people from the dead. The purpose of these miracles was to glorify the Father whom he loved.
Through his perfect, sinless life, expressed in his obedience to the Father "unto death" (Philippians 2), Jesus accomplished through his perfect obedience what the first Adam failed to accomplish when he followed Eve in her disobedience to God's command. Jesus thus became the last Adam of whom Paul spoke in 1 Corinthians 15.
Jesus is not always sitting comfortably at his Father's right hand, however. We know, for example, that Jesus will return someday to earth in glory and majesty to bring history as we know it to an end by defeating Satan, sin, and death once and for all. Once we understand Jesus' right to be seated next to God's throne (an allusion to Psalm 110:1), and so as not to treat Jesus' sitting at God's right hand too literally, we can readily understand the freedom he has to exercise that power once again by rising from his seat.
As for Jesus' standing in the vision Stephen had at his stoning, I'd like to think Jesus was standing so as to welcome Stephen into his presence when at death Stephen's spirit departed from his body.
The point is, Jesus is an active co-regent with his Father. Whether he sits in making intercession for the saints (Hebrews 7:25), whether he stands to welcome a faithful martyr into his presence, or to return to earth as the commander in chief of the Lord's army, Jesus, whether seated or standing, could say of a truth,
All authority in heaven and earth has been given to me (Matthew 28:18).
Acts 7:55 tells the story of Stephen, who was the first disciple to be martyred in the name of Jesus. What is interesting about the account of Stephen, aside from being the first, is that his death follows almost exactly what Jesus foretold in The gospel of Mark:
9 "But be on your guard. For they will deliver you over to councils, and you will be beaten in synagogues, and you will stand before governors and kings for my sake, to bear witness before them. 10 And the gospel must first be proclaimed to all nations. 11 And when they bring you to trial and deliver you over, do not be anxious beforehand what you are to say, but say whatever is given you in that hour, for it is not you who speak, but the Holy Spirit. 12 And brother will deliver brother over to death, and the father his child, and children will rise against parents and have them put to death. 13 And you will be hated by all for my name's sake. But the one who endures to the end will be saved. - Mark 13:9-13 ESV
Stephen died proclaiming the gospel and was faithful doing do just as Jesus has commanded of his disciples. So, Jesus stood to receive his faithful servant.