How are 'salvation' and 'the Gospel' related?
Salvation is important, but it isn't the entirety of the Gospel. My mind goes to the euphemism "Full Gospel" that some Pentecostal types use to describe themselves, insinuating that garden-variety evangelicals avoid the parts of the Gospel that include the Holy Spirit as a hands-on day-to-day player in our lives today.
An overly-salvation-centric Gospel presentation (yes, there can be such) will underplay discipleship and learning about God as a whole. Most folks don't have that problem, since a salvation message isn't PC, requiring folks know both that they are sinners in need of a savior and that a Savior is there at the ready to accept them as-is. It's easy to sugar-coat that issue in a secular setting, but it's also easy to get off on a fire-and-brimestone tangent, where we focus on our sinfulness and our need of a risen Savior.
At issue here is the language of salvation, and the difficult doctrine of forensic justification. For those in the Catholic and Orthodox branches of Christianity, 'salvation' encompasses the sanctifying work of Christ. In those theological frameworks, it would be impossible for a salvation-centric gospel presentation to not include discipleship and spiritual disciplines.
If my reading of Calvin (the Reformer with whom I am most familiar) is correct, he is in line with this understanding of the notion of salvation. The two graces--justification and sanctification--are given together, and only given in Christ. Salvation is being 'in Christ,' which necessarily includes both.
Such an understanding of salvation seems at odds with many evangelical ecclesiologies (including seeker-sensitive ecclesiologies), which seem to separate the work of discipleship from the work of salvation. If salvation necessarily transforms us and the world around us, then the Church could not be the Church without fostering discipleship and spiritual disciplines. As it is, those Churches that view the sanctifying work of God as accidental to our salvation undermine not only the Gospel, but the reality of our union with Christ.
I would disagree, then, with what (I think) Mark is saying. The issue is not that the Gospel is larger than salvation. It is rather that our concept of salvation is too small. We are 'saved,' we are 'being saved', and we 'will be saved.' Our salvation produces, encompasses, and is perfected by our discipleship and our continuing intimacy and union with Christ.