Good Q. There is a deep meaning to this that takes some time to realise - a lifetime! It's expressed through Rom 6:11.
Even so consider yourselves to be dead to sin, but alive to God in
While we have been included in Christ's ascended life, made 'alive' in a whole new way, we must continue to plumb the depths of how we have died.
Sin had hold over us, as we could not do anything to be free from the penalty of death - ever! Paul wants us to understand that sin's hold is no longer. We are freed from being a prisoner to sin and death... through Jesus. To the point that Gal 2:20 expresses
I have been crucified with Christ; and it is no longer I who live, but
Christ lives in me.
Any time we fall into old ways of sin, it is because we have lost sight of who we are in Christ. We have offered ourselves again to the law of sin and death - not that it has hold over us, but we have chosen, through carelessness or rebelliousness, to live out of the old man, not the new man in Christ.
An analogy would be the how Israel wanted to go back to the 'leeks and garlic of Egypt' rather than forge ahead to the new land. (Num 11)
We might picture it this way. We were chained to this world and law of sin and death. Jesus has smashed the chain - totally freeing us, but some of the links remain attached to our ankle. We can run as far as we like from the old, but the baggage (links) of who we were - slaves to sin, are an ever present reminder.
As we joyously consider the new life, let us also consider that it is only lived to the extent that we grasp how dead the old one is!
We look forward to our change - the remaining links have disappeared and we are finally like He is!