The Greek verb kephalaioō (from kephale, G2776, head) has two usages: (1) to sum up or bring to a main point (recapitulate), and (2) to hit on the head. In Mark 12:4, it is used in the Parable of the Wicked Tenants: 'They struck him on the head [ekephalaioōsan].' In Romans 13:9, Paul uses the related form anakephalaioutai (to recapitulate/sum up): 'Love is the fulfillment/recapitulation of the law.' The word literally means 'heading up' — either gathering to a main point or targeting the head.
Paul's use of the recapitulation concept (anakephalaioo) in Romans 13:9 and Ephesians 1:10 is one of the great theological insights of the New Testament. In Ephesians 1:10, God's eternal plan is to 'anakephalaiōsasthai all things in Christ' — to sum up, unite, and bring to a head all of reality in the person of Christ. History is not chaos; it has a kephale (head) — it converges on Christ. This is the cosmic Christ as the recapitulation of all creation, which Irenaeus developed into the great theological doctrine of recapitulatio.