Organic Connection
His resurrection is the representative beginning of the resurrection of believers. In other words, the term seems deliberately chosen to make evident the organic connection between the two resurrections. In the context, Paul's "thesis" over against his opponents6 is that the resurrection of Jesus has the bodily resurrection of "those who sleep" 7 as its necessary consequence. His resurrection is not simply a guarantee; it is a pledge in the sense that it is the actual beginning of the general event. In fact, on the basis of this verse it can be said that Paul views the two resurrections not so much as two events but as two episodes of the same event.
Richard Gaffin, Resurrection and Redemption: A Study in Paul's Soteriology, pg. 35