Paul is writing a letter to Ephesus, the usage of "we" in chapter 2 is not mostly a general we, or as you put it (believers per 1:19), but are those with him, having come so far in Christ, or "who first trusted in Christ" (per v12). For he distinguishes the many early "we's" from the "ye" which are the people to whom he's writing (begining in v13 "in whom ye also trusted..." emphasis on ye also, as distinct from the early we's). Tychicus, who is a beloved brother, and faithful minister in the Lord, may be an example of one of those in the "we," for Paul says Tychicus will make known unto you all things. For, only a minister of God can make known all things 6:21, and only he who has purged himself from these (vessels to dishonor), is sanctified, and meet for the masters use, and prepared unto every good work. Those to whom the early "we's" refer along with Paul, are not those to whom he would need to write things like 4:25-32, among plenty else. Furthermore, to the we, God was already abundant in wisdom, and had already made known to them the mystery v8,9. But for the "ye," these are the very things Paul is praying God would make known v17,18. You will see here that the we's eyes already have these things made known to them. The ye, to whom Paul is writing, needs their eyes enlightened to these things.
So what Paul is doing here is setting the we, whom he is among, as examples to the ye. So that his exhortations have some present example. Paul does this often, in plenty of other places which people read as if they are general we's, not noticing that he distinguishes in other writings as well 'we' from 'ye.' Easy places to see that the 'we' and the 'ye' are not always all Christians, but a distinct group, is quite a bit of Galatians, Corinthians, and other places. Other places can also be found like He 6:9,11; and consider 9:14 The writer's conscience has been purged already, hence "shall the blood of Christ purge your consciences from dead works. Furthermore, 12:4, those to whom he was writing had not yet encountered the blood, striving against sin. So then, read this in light of the whole chapter 12, and his admonishments to them, who had not yet resisted unto blood striving against sin. For when they had, that blood would purge their consciences from dead works, as he said in chapter 9.
I think many, including almost all theologians I've ever heard/read, treat these letters like treatises, when they are letters. They have a sender, and those with him, or with whom he more perfectly identifies. They have receivers, to whom the writer(s) stand as examples, and all who have progressed so far spiritually. They have third parties, which are also referred to. They have statements that apply to all men, some to all believers, some to all the receivers, some to the writer, some to the holy men, some to the unbelievers, etc. Not all statements are just general statements about all professing Christians. What you will find in understanding this, is many of the great things which many consider to be "imputed" to wicked men, and babes, and all so-called believers, are not about them at all, but about the holy men, with whom the writer identifies, whom he normally categorizes or distinguishes from the receivers, as standing examples, and thus beacons to be striven toward.
