Half-way through the letter we realise that chapters 1 - 3 are all about God, and 4 - 6 are about our response. Kind of 'because God is ... I urge you to respond thus ...'. Verse 2 briefly says to do it with good character, and verse 3 calls for us to make every effort.
That effort to keep the unity can be considered in two ways. Firstly in any church with N people, there are (tongue in cheek) N-squared ways of doing things! Clearly we need to find our collective calling - the Spirit's direction for us as a body of people. That takes effort (!): covenanting together requires us downgrading our own agendas so that we might upgrade our role in the corporate agenda.
Secondly unity takes effort because it requires us to physically show up. Our virtual world provides benefit, but we know it cannot replace actually being together. We need to be there in our life together: be it our corporate worship, times of discerning (e.g. church meetings), praying together, as well as mission initiatives taken on by the whole church. We are blessed with a high percentage serving in some way: which is great because we continually need calling to translate into commitment and service, i.e. pitching in.
The Spirit may call us to a joint purpose, but He does it through our diversity of members. We are not all clones, and have different gifts. As per this message the 5-fold gifts enable women and men to emerge who can help lead us in the plans of Jesus. These Spirit-gifted people equip us in our works of service, but as v13 makes clear we all have a role to play (not just a few specials).
The goal is being built up together in Jesus, drawing others along the way, all towards fullness in Christ. This matches one of our current key discipleship habits, that of aiming to be ever closer to Jesus. We should never be content with the status quo of our spiritual lives, but rather always seek to be closer to the Lord in what we do, what we understand, and what we experience.
This is the maturity talked about in v13 & 14. Jesus' model of discipleship was to enable his followers to learn to stand on their own two feet ... from which they could then disciple others. A sign of maturity is that we take responsibility for our own discipleship - finding our rhythms and diet for input and exercising faith in service. The alternative is to be tossed about by the waves and the wind!
As a church we wish to take God given life out to the city, declaring and demonstrating that 'but because' of Eph 2:4. We want to do that sustainably, so we say "stay close to Jesus, and be led out in His mission". V16 concludes with us all being held together in Jesus, doing work in the community for Jesus. This is our collective calling, our God given purpose, which we do in response to God described for us in chapters 1 to 3.