v1-3 - You've been called by God, and although that calling was not based upon your own actions, your actions moving forward must reflect your calling.
Put others first;
Do the hard work necessary to keep the Spirit's unity, being united to those who long for peace as you do.
v4-10 - We can be unified as Christians because we have one God and Father, and He has given us grace through Christ Jesus.
v11-16 - Christ has made a massive investment in you, first providing apostles thousands of years ago, and now pastors and teachers, all of whom have the same objectives: to equip you for these things:
Acts of service;
To build up the church;
To know what you believe and why you believe it, so that you're not tossed around any more on the chaotic sea of society.
Notice, however, that although Christ is the one who's made this investment, this process of being built up by Him is not a passive experience. Rather, you're called to take advantage of what you've been given to grow.
v17-32 - Step one in this growing process is to stop living like a pagan. Actually, this isn't just step one, as it's a continual process of stopping since your old nature is in a continual process of dragging you back into sin.
Pagans are wandering in the dark because their thinking is futile (v17), so consequently they've literally become callous, which drives them to over indulge in every sensual pleasure they can find.
This is not what you've been taught by all the resources the previous passage told you Christ has given you.
The Christian life can be summarized in these two brief statements:
"To put off your old self,"
and "to put on your new self (v22-24)."
The remainder of this chapter, starting with the word 'therefore' in v25, indicates what the new self that you're putting on should look like.