The Letter to the Ephesians was probably written a considerable time after the death of St Paul. In the meantime he had fallen out of favour and then regained his popularity. People were clamouring for more of his teaching and Christians of long-standing found themselves hunting through their lofts, packing cases and blanket chests, looking for some of St Paul's missing letters which had been circulated long ago around the young churches in his care and then discarded or forgotten.
If losing a letter from St Paul sounds sacrilegious or careless then, in fairness, we need to remind ourselves that St Paul never crafted his letters as though he intended them to be kept for posterity. He dictated them, often in great haste, in a kind of shorthand that our careful English translations paper over and conceal. He was addressing immediate problems and often he was writing to people who disagreed with him intensely. Little wonder, then, that some of his letters did not survive, and that others survived only in fragments.
It's fashionable now to claim that St Paul invented Christianity, reshaping the original teaching of Jesus into something quite different but, in fact, during own his lifetime St Paul never had much influence on the shaping of Christianity. Like so many writers and artists, his enduring reputation was forged only after his death. At the time, other people appeared to win the arguments and only with the benefit of hindsight did Christians come back to St Paul's teaching and rediscover him as one of the Church's greatest ever theologians and pastors.
The writer of the Letter to the Ephesians seems to have been one of this new generation of fans. He had read all – or almost all – of St Paul's surviving works, and probably St Luke's biographical account of St Paul's ministry too. He may also have had in his possession some fragments of a letter written by St Paul to the Church in Ephesus. Around these he constructed what he believed St Paul would have wanted to say if he were writing to the same church now.
It's clear that he believed St Paul would have been greatly upset by disunity within the Church, so he makes a touching plea that members of his congregation – or of the different congregations in Ephesus – might bear with one another in love, making every effort to maintain the unity of the Spirit in the bond of peace. 
The writer is a realist. He knows just how difficult it is for Christians to get along even with one another. It takes every effort that we can muster to bear with one another's faults, failings and foibles. Not only that, but it takes every effort to reach out to one another across the divide between different generations, genders, cultures and races. Being one family under God is a nice idea. We talk about it when people are baptised, and it's the cosy concept which underpins our family services. There is even an organisation that has been set up to help us become more 'family friendly'. But the very fact that we need an organisation to help us do this proves what the writer of the Letter to the Ephesians already knew. Being one family is far from easy. In fact, he says it can only be achieved if we are united to one another by God's Spirit and if we allow God's deep peace, which passes all understanding, to bridge the many divides which separate us. Just as God is undivided, so we too can be undivided – but only through the grace of God, bestowed on us by Jesus Christ.
The writer embarks on a little digression at this point, quoting a creed used by the early Christians, which he uses to prove that Jesus Christ gives us the gifts that we need in order to live and work together in unity, and that these gifts are powerful enough to overcome every obstacle. Echoing the teaching of St Paul himself, he also says that we don't necessarily receive exactly the same gifts – but instead we are equipped by the Spirit according to the measure that we need, including any gifts we might need to carry out special tasks that have been assigned to us such as teaching, or evangelism, or pastoral care. But his key point is that – one way or another – all of us are given gifts to help us do two things. The first thing is the basic work of Christian ministry – which is, serving God in our daily life and work, whatever that might be. The second thing is the building up of the body of Christ, where we all share the same basic responsibility to help one another become more like Jesus Christ – and not just to become a little bit more like Jesus, either, but to measure up to the full stature of Christ; to think, and speak, and act exactly like him. Nothing less will do!
That incredible image – of being exactly like Jesus Christ himself – brings us back to the writer's main theme of getting along with one another. We mustn't be immature or behave immaturely. Instead we must strive for complete maturity in every aspect of our faith and life.
And we mustn't allow ourselves to get drawn into power struggles or devious schemes. I think that what the writer means by his colourful references to trickery, craftiness and deceitfulness is the tendency which all of us have of trying to persuade other people – even in church meetings – to do what we want rather than what God wants. When we're really serving our own interests – trying to keep things the way we prefer them to be, or to protect our own role in the church's life, or simply to have a quiet time and avoid being shaken out of a comfortable rut – that's not something we're likely to admit, is it? Instead, I guess we're all tempted to dress up our motives as something better and more noble than they actually are, to claim that we're only concerned for the best interests of the Church, or for the effectiveness of the Church's work, or that the will of Jesus Christ himself might be done. Of course, the only mature approach is to be honest both with ourselves and with others, and to confront our true reasons for doing things or for resisting change.
There is a difference, however, between speaking the truth and speaking the truth 'in love'. In many churches I have come across people who prided themselves on always speaking the truth, and they have seldom minded how obnoxious they were – or how many people they upset – in the process. After all, they had the perfect excuse for being nasty. They were only speaking the truth.
Interestingly, I have found that these same people didn't usually like it when others spoke the truth to them. Plain-speaking wasn't a two-way street! Nor were they always humble enough to recognise that they might still be wrong even when they were absolutely convinced that they had truth on their side.
The writer of the Letter to the Ephesians had met people like this too. That's why he's careful to qualify his statement by adding that we must speak the truth only in love. Love is always honest, and it can be angry when things are wrong and need to be put right. But a person who speaks the truth in love will be patient and kind, and will keep his or her self-control even when other people are losing theirs. Above all, speaking the truth in love is about being positive and constructive. It's about seeking to build something better rather than simply knocking things down. It's aim is to make the whole body stronger and more effective, not to cut others down to size, or teach them a lesson, or undermine them. And the writer concludes by reminding us that the mark of an effective church is always first and foremost that it is a loving church.
To sum up, then, what – according to the Letter to the Ephesians – should we look for in a healthy, happy church? We should look for a group of people who are making a real effort to find a sense of togetherness and shared purpose that will bridge all the differences between them. We should look for people who are keen to serve God in their daily lives and to encourage and build one another up whenever they meet together. We should look for people who are really striving to get the best out of life by measuring up to the pattern set for us by Jesus Christ. And we should look for a group of people who try to decide what to do with honesty, integrity and love. Then we shall have a church which is worth belonging to, which builds us up and helps us to grow. If we belong to a church like this we shall be able to do the works of God and we shall find ourselves working not just for the kind of goals which are here today and gone tomorrow, but for goals that will endure forever.
 Ephesians 4.25 - 5.2