"Wherefore when He cometh into the world, He saith, Sacrifice and offering thou wouldest not, but a body hast Thou prepared me." (Hebrews 10:5)
So God sends Jesus, who in turn forms the church upon His death, resurrection and ascension. These two acts coincide with the first two of Aristotle's "four causes". Jesus taking bodily form being the "material cause". The subsequent formation of His figurative "body"—the body of Christ—being the "Formal Cause". What we're getting at here is the actual and overarching definition of what it means to be human in this world—with reference to God. And all that that entails. Which brings us to the third cause: the Efficient Cause. I might be playing fast and loose with Aristotle here. Hear me out.
In part three, Jesus' prayer in John, chapter 17 lists the qualities that a church should possess. Essentially oneness. Oneness with Jesus and, at the same time, oneness with His Father. "That they all may be one; as Thou, Father, art in me, and I in Thee, that they also may be one in us: that the world may believe that Thou hast sent me." (verse 21)
But how to get from there, to a worldwide, cohesive and cogent, active Christianity? One that is "full of mercy and good fruits, without partiality, and without hypocrisy" (James 3:17)? Jesus had to show it. He had to be that "Efficient Cause". He had to live out the perfect life, of service, rejoicing, gratitude, etc. that we would know who to look to, when living our own life in the world at large and with others. There comes a time, if you haven't already experienced it, where all you will want to do is segregate yourself from the rest of society. I don't mean to sound stark and harsh here, but the world is an incredibly lonely place without Jesus. But! We have Him. And we have each other. "There is a friend that sticketh closer than a brother." (Proverbs 18:24) That friend is Jesus. And if anyone else chooses to act along the same lines, they live out that closeness, companionship and friendship, that Jesus embodies.
John's Gospel says something very powerful regarding the mindset Jesus had after His last supper (13:3): "Jesus knowing that the Father had given all things into His hands, and that He was come from God, and went to God; He riseth from supper, and laid aside His garments; and took a towel, and girded Himself. After that He poureth water into a bason, and began to wash the disciples' feet, and to wipe them with the towel wherewith He was girded." This is the key: He served. "Greater love hath no man than this, that a man lay down his life for his friends." (John 15:13) We might be inclined to think that "laying down our life" means to die for someone or for a cause, but more often than not, it means the giving up of our time and our plans and our outlook to help those whom God has placed in our path. But before we go any further, look at what Jesus knew He was in possession of when He got up to serve, to live it out. It says that "the Father had given all things into His hands" and that He knew from where He had come and to where He was going. Those three things encapsulate all our human yearnings. Jesus was willing to die for us. He was also willing to serve and to show His love in ways no one expects. The small ways of kindness and friendship and understanding and empathy. These things are worth a thousand words and they are what make up a life.
Now, our part in the "Efficient Cause" of the formation and maintenance of the body is the same as Jesus: "For, brethren, ye have been called unto liberty; only use not liberty for an occasion to the flesh, but by love serve one another." (Galatians 5:13)
"And again, The Lord knoweth the thoughts of the wise, that they are vain. Therefore let no man glory in men. For all things are yours; Whether Paul, or Apollos, or Cephas, or the world, or life, or death, or things present, or things to come; all are yours; And ye are Christ's; and Christ is God's." (1 Corinthians 3:22, emphasis mine)
We, like Jesus, came from God, are going to God and (*gasp*) possess all things. So, live it out. Serve. Love. Give. I would equate this active mindset of service and caring more for others than ourselves with Aristotle's "Efficient Cause" as applied to the Christian walk.