The second way to understand the two Commissions is the standard in Reformed circles, as far as I can tell. The view is that the first (Genesis) Commission still stands, and is still basically definitive for our understanding of God’s intentions for humankind, even fallen humankind. Human beings are still commanded to fill the earth and subdue it, with every advance in culture, science, and technology which this implies. Christians are to be particularly involved with and interested in these things, since they receive them not only as the apparently obvious ingredients of a satisfying human life but also as the command of God. This is not at all to deny that the fall has marred every aspect of what human beings do in response to this Commission. It is, however, to say that the command still stands nonetheless, and that it ought to be obeyed, despite the fact that it can never be obeyed perfectly. Something of value will be kept in all human striving that corresponds to this Commission. The concept of common grace generally comes into play here.
The second Commission is understood against this background. Given the broken nature of creation following the fall, the first Commission cannot be fulfilled, in the sense of fully and perfectly executed, but human beings alone. God must step in to make it possible again, and he does so in Christ. Christ’s work is about the redemption of all creation, and its restoration to its original potential. Therefore, Christians are bound not only to engage in first Commission work, but also to join in the second Commission task of preaching Christ, through whom alone the first Commission can be fulfilled (eschatologically, for the most part). As an aside, a good introduction to this view is the little book Creation Regained by Albert Wolters.
This view also has much to recommend it. Not least, Christians who hold it are likely to live more interesting lives than those who hold the first view, and this may well have the effect of making their evangelism more effective; their engagement with the ordinary work of humanity has the potential to commend the gospel. Independently of this, they are surely correct to see more in Genesis 1 and 2 than a wistful memory of a long-dead world. With this perspective, advocates of the second view are equipped to avoid the secular/sacred divide that more or less inevitably follows from the first view. Still, I’m not sure this view has it completely right. I worry that it has the potential to make the gospel of Christ merely a means to an end, and the lordship of Christ a secondary rather than a primary concern. This is a danger, not an actuality - I don’t think people actually go this far, or at least not explicitly. But I think it is a valid concern; the gospel is not an afterthought. Add to that, I’m not sure the framework of creation restored can contain the eschatology of the Bible - the end promised to us seems, to me, to be much more than the beginning.
The third view, which is mine and therefore saved to the last so that it seems more impressive, rests on the insight that chronology is not always the key. The second Commission, on this view, is really the first, and the first is the second. To clarify, we’ll call them G-Commission (for Genesis) and M-Commission (for Matthew). Rather than seeing G-Commission as basic, and M-Commission as a necessary addition in the face of sin, the third view sees M-Commission as basic. The spread of the kingdom of Christ, through the evangelization of the nations, is - and always has been - the central purpose of everything that exists, including human beings and everything that they can do or produce in conformity to the G-Commission. This is not to devalue the G-Commission; rather, it is to provide it with a secure place. Although advocates of the second view see value in both Commissions, I do not know how they can hold them together. It seems to me that either one or the other will necessarily be without foundation and arbitrary. It is all very well to say that the G-Commission is still in force, but I wonder what that can even really mean after the fall. And I wonder what relation it can really have to the M-Commission. By contrast, this third view holds the two together because it sees the fulfillment of the G-Commission occurring as, and only as, human creativity is brought under the lordship of Christ. This does not mean that cultural artifacts and the like which are created without reference to Christ lose all their value; it simply means that Jesus is Lord over them whether their creators like it or not, and so they can brought in some way - whether by appreciation or critique - within the orbit of the church as the community which knows and bows to his Lordship in the here and now. (This involves a rethinking of common grace; it is not a kind of basic grace which is independent of the gospel grace of Christ - rather it is the overflow of the gospel, or perhaps just the gospel as it applies to those who do not know it or acknowledge it).
I think this is a better way of understanding the relationship between the G-Commission and the M-Commission. It keeps the main thing - the Lordship of Christ and its recognition amongst the nations - as very definitely the main thing, and it securely grounds everything else by relating it to this great divine project. It fits better with the shape of the doctrine of creation, as I understand it. Most importantly, I think it lets us live as Christians - set free from every concern which is not Christ, whilst recognising that Christ means more than we might initially think.
(It occurs to me, at the conclusion, that this whole post is probably just a way of saying that I am a supralapsarian; if that doesn’t mean anything to you, lucky you).