It is obviously the case that we should make progress in the Christian life, but personally I don’t think that is what Paul is saying in this verse. Rather I think he is pointing his readers forward to the experience of complete unity that they will experience at the second coming of Jesus. There are three benefits of the final state of union mentioned here.
The first one is ‘unity of the faith and the knowledge of the Son of God’. ‘Faith’ refers to doctrine, to what we believe, and this is a reminder that doctrine will be taught in heaven. Our understanding that we have about God and Christ will be enlarged throughout the eternal ages. Doctrine is not dry, although sadly it can be presented dryly, although it may also be the case that we perceive doctrine as dry because our souls are dry as a consequence of grieving the Spirit. I am not referring to intellectual awareness of doctrinal opinions at the moment. What Paul has in mind is teaching by the Holy Spirit and there is coming a day when that teaching will be appreciated fully by all the people of God.
Paul focuses on one teaching of the faith in particular – the knowledge of the Son of God. We will know more of Jesus increasingly in heaven. Perhaps we have heard about the desire of Philip Melanchthon on his deathbed, that he was looking forward to understanding in heaven the relationship of the two natures in the person of Christ. The knowledge of Christ will also be more immediate, because we will be physically in his presence, glorified and made like him. But we will still need to be instructed by Christ and enlightened by the Holy Spirit.
The word that Paul uses for ‘knowledge’ is a strengthened form and so means experimental knowledge. Paul himself had first known Jesus after the encounter on the Damascus road. Three decades late we find him still wanting to know Jesus (Philippians 3:10: ‘That I may know him [Jesus], and the power of his resurrection, and the fellowship of his sufferings, being made conformable unto his death’). This life is a growing appreciation of what Jesus has done for us and does for us. I suppose it could be likened to a poor girl who marries a king and discovers it will take all her life to appreciate the extent of his riches and power. We discover that Jesus is forgiving, compassionate, caring and sweet. But what we discover of him in this life is but a foretaste of our knowledge of him in the eternal world.
There is a beautiful story told of John Owen, the Puritan theologian. It happened that he had just finished his book called The Glory of Christ when he suffered an illness from which he died. The proofs of the book were brought to him the day before he died by a minister called Payne. Owen told Payne that he was glad to hear that and then said, ‘But, O Brother Payne, the long looked for day has come at last when I shall see that glory in a manner than I have ever done yet, or was capable of doing in this world.'
Of course, our knowledge of Christ in the eternal world will be constant, unlike now when it is often interrupted by the world, the flesh and the devil, or by necessary factors of life. It will also be comprehensive, in the sense that it will be balanced and we will have insight into every aspect of his person and work. Further it will be both corporate and individual, because we will share the benefits he brings to all his people and also enjoy them at an individual level. The manner of appreciating Christ will be contemplative in the sense that we will behold him with our eyes, our minds and our hearts, a contemplation that will be both immediately transforming (when we shall see him we shall be like him, for we shall see him as he is) and increasingly bring heavenly joy and delight.