Ephesians 2:5-7

even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved— and raised us up with him and seated us with him in the heavenly places in Christ Jesus, so that in the coming ages he might show the immeasurable riches of his grace in kindness toward us in Christ Jesus.

-Ephesians 2:5-7

Going by the chiastic structure, this is the climax or main point of this section.  We are saved by grace.  After going on about our hopeless previous state before being saved, there's a shift and we are told about how God steps in.  We are miraculously saved from that which we had no hope.  "-by grace you have been saved-".  It is only by grace that we have been saved.  This free and unmerited favor of God is the only thing that saves us.  He has stepped in, "But God".

So, what else does he do?  "and raised us up with him and seated us with him in the heavenly places in Christ Jesus".  We are raised with Jesus and we are seated with Jesus.  In the last chapter, Paul has already told us about where Jesus has been seated.  God the father has "seated him at his right hand in the heavenly places, far above all rule and authority and power and dominion, and above every name that is named, not only in this age but also in the one to come".  We are seated along with him.

Why would such a thing be done for us who were dead in our trespasses and sins?  We are told why in the next verse, "so that in the coming ages he might show the immeasurable riches of his grace in kindness toward us in Christ Jesus".  God wishes to use this as an example of how great is his grace in kindness toward us.  This is an example of how great God is.  I guess you can't always show a quality or character trait of someone without an example to point to.  You can't just tell others how loving you are without some kind of reason to back it up.  God's saving grace that saves us out of our deadness is an example of how great God's grace really is.