The converse of this is that a church may have a defective constitution and yet preach the gospel. To take one example: the current effective constitution of the Church of Scotland is theologically minimal. While giving a courteous nod to the Westminster Confession, in practice the Church is bound to nothing except the doctrine of the Trinity and 'the Scottish Reformation'. Because there is no standard of theology, the most bewildering theological pluralism prevails. The constitution does not safeguard the gospel. Yet, there is no denying that the gospel is preached: fully and brilliantly in some pulpits, adequately in others, minimally in yet others (and probably not at all in some).
In any judgment of a church then, we have to look beyond its actual constitution. Some with admirable constitutions do nothing by way of evangelism; while others, with radically defective constitutions, do a great deal.