The two comings of Christ

Psalm 110 clearly implies that there would have to be two comings of Christ:

• He was appointed to rule "out of Zion", "in the midst of [his] enemies". Whilst he ruled, he would have enemies to conquer, to be put under his feet (verse 1). So clearly, this must be before he finally banishes all evil and renews the creation.
  
  
• But, David was speaking of something that as yet was in the future - the Messiah's reign had not yet been inaugurated.
  
  
• It is clear, too, that "Zion" cannot be the literal Jerusalem. Some interpreters say that it is so, and that this talks of a future millennium. Not only is this contrary to how the Psalm is used in the New Testament (e.g. Acts 2:34-35), but it would contradict verse 1, which says that the rule is from God's right hand. The Christ rules from God's right hand, which is Zion - the place symbolising God's presence and strength.
  
  
• More than that, he is a priest forever, of the order of Melchizedek (verse 4). A priest deals with the problems caused by sin and mediates through prayer and sacrifice. But, after Christ's coming in glory, there will be no need for any work of priesthood. So again we see that we're dealing with a time whilst this present age continues.

So, the Messiah is conquering over a sinful earth and providing mediation for his people after having ascended to God's right hand. That's only possible if there's a first coming which isn't his coming in glory, before the coming which is in glory.

I also found it interesting to note that God speaks twice: once to appoint the Messiah as a king who will defeat his enemies and receive willing service from his people, once to appoint him as a priest (who will deal with his people's sins).