Well, come on, what could possibly be wrong with the insistence that all of our thoughts and actions about every aspect of our lives - politics and science and economics and education and childrearing and art and work and sport and everything else - should be determined in relation to the gospel?
Nothing at all. So far, so good. Three cheers, and then some.
But there's a potential problem lurking in the background. The key question is this: What do you think the gospel is?
Suppose we get the gospel right. Suppose you believe that the gospel is the glorious annnouncement that Israel's God has at last returned to Zion (Isa 40:9) in the person of Jesus of Nazareth, who has been declared with power to be Israel's true King and the World's true Lord and Judge (Rom 1:1-6); that this Man is David's greater Son, and has now been exalted to sit on David's throne (1 Tim 2:8); that therefore the creation which was once ruled by a rebellious man of sin and dust and death is now ruled by a perfect Man of righteousness and glory and life (Gen 1-3; Rom 5; 8; 1 Cor 15); and that this Man invites and commands all people and all nations to bow before him and receive from him forgiveness of their sins, adoption into God's family, empowering by the Holy Spirit, and a renewed vocation to bring every aspects of their lives into conformity with God's inspired and infallible word, the Bible (I'll leave you to dig out those biblical references - I'm running out of space).
This being the case, there is no problem with affirming that every aspect of our lives should be determined in relation to the gospel.
However, suppose we get the gospel wrong. Or, if not wrong, perhaps a little shrunken. Suppose, for example, we think of the gospel in narrower terms, as the proclamation that we're sinners before a holy God and a righteous Judge, and that God has provided in the crucified and risen Jesus Christ the salvation we need to be put right with him. This is gloriously true, of course, as far as it goes. But it will create all kinds of problems if we identify this as the gospel, and then start to think of all the other aspects of our lives.
The problem is that it is not at all obvious how this message of individual salvation in itself has much relevance for politics and science and economics and education and childrearing and art and work and sport and everything else. If we think of this as "the gospel," we'll be right in what we explicitly affirm but wrong in what we implicitly deny. For by conceiving the gospel too narrowly, this view overlooks the fact that the gospel has any relevance beyond the salvation of individual people, since it mistakenly identifies one (vital and glorious) aspect of the gospel (the promise of salvation for sinners) with the gospel as a whole (the declaration of the Lordship of God in Christ over all creation).
To take one example: if we ask what relevance this restricted vision of the gospel has for secular work, we'll probably struggle to find any connection beyond the (true and important) insistence that we should try to evangelise our colleagues. We're unlikely to grasp the rich Reformed and biblical doctrine of the dignity of secular vocation: the wondrous truth that all of our work - whether banking or preaching or childrearing or busdriving or whatever - has dignity in the eyes of God not merely because it is what he gave us to do, but also because it is what He Himself is doing in the world through his redeemed-in-Christ human vicegerents to fill and subdue all creation to his glory (Gen 1; Ps 8; Heb 2; etc).
So there's nothing wrong with being gospel-centred. We just need to make sure that we get the gospel right.