Rev. Gordon is nowhere near a gnostic, for what it's worth. He's also using the word 'established' in a more technical sense (as in, the anti-establishment clause of our 1st Amendment). I'm familiar with Leithart and the 'Federal Vision' crew and find their rejection of the distinction between the invisible church (election) and the visible church (covenant) to be massively incorrect (mainly because of the implications on justification by faith alone) -- and based on a misunderstanding/misreading of recent Dutch Reformed (like Schilder) who had a slightly different understanding of covenant and election than we tend to. "Who says covenant says history, who says election says eternity." This all goes back to one's Covenant Theology, which is why I so appreciate Kline and VanDrunen. Get the beginning wrong and--like a pilot that starts off 1° off course--the further one goes, the further from the target desination one strays.
There is no such thing as "Christian work" unless you mean Word and Sacrament ministry. The gospel is _news_ it is not _action_. There is good work and there is poor work. That the work is good does not make it Christian--and often Christians produce work just as shoddy as the world (if not worse -- ever listened to CCM?). A pagan can deliver a just ruling. A pagan can fix my plumbing. A pagan can represent me well in court or give me an accurate diagnosis for a malady. This is due to common grace. A Christian who does good work does it 'as unto the Lord' but that doesn't make it "better work" per se. Being a Christian may give me a higher motivation to improve my working, a different motivation for pursuing excellence--but that doesn't make it 'Christian' work.
We are pilgrims here, not conquerors. That's not "loser" talk--it's the talk of the faithful (Heb. 11) whose affections are set on heaven (Col. 3). We do not overcome by capturing institutions and all of culture for Christ. He has already conquered all things (having accomplished the Covenant of Works for us, having already inaugurated the kingdom, yet we wait for its full consummation at his return). There is _nothing left to be done_ except what is provisional, earthly, and--dare I say--_secular_ (i.e., temporary) and of the common kingdom. Unless we're talking about Word and Sacrament ministry which is the work of the redemptive kingdom and stands alone as _sacred_ work.
I do hope you'll consider giving the three VanDrunen books a read, even if only to gain a full understanding of what (it seems) you're rejecting (2K).