Growing up, I used to think that looking believingly on Christ's death for my forgiveness was the first thing I ingested as a Christian and then got past - that you grasped the gospel, and then moved on to mortification of the old self and what I called "being used" for God. I thought of it in two stages, and, in my experience, many other Christians do as well.
For different reasons, I think this is a mistake - the relationship between these two non-optional dimensions of the Christian life is different. In the NT, there is no "and then moved on;" the very first thing you learn as a Christian is constantly, explicitly invoked as the reason, basis, and efficient cause of everything else we are required to do as Christians. One of these days, I'm going to put together a list of NT passages showing this; but for now, two quick examples:
Romans 8.4, where Paul says that Christians who walk by the Spirit fulfill all the requirements of the OT law, is hugely significant for how we read and interpret all the OT. But notice how quickly it follows the beautiful affirmation of no condemnation for us in Christ in v. 1 - and, in fact, in the Greek, v. 4 is syntactically dependent on v. 1. (V. 1 forms its own sentences, but everything in vv. 2-4 needs v. 1 to make sense.) Paul directly connects walking by the Spirit and the requirements of the law being fulfilled in us with the ground-floor, entrance level "no condemnation" proclamation of the gospel.
Again, in 1 Peter, the apostle calls on us to be holy and uncomformed to the world (v. 16), conducting ourselves in fear before the God who judges us according to our works, knowing that . . . and I wonder how you might finish the sentence? What do we keep in mind as we live out holy lives, mindful of the Judge we'll soon face? Peter ends it in v. 18 with, "knowing you've been redeemed by the precious blood of Christ"! Something similar happens in 2 Peter 1.9: those lacking "these qualities" of mature Christians in vv. 5-7 are not told to get on and produce them, but brought back to square one: they've forgotten their forgiveness (v.9).
I have found it edifying to meditate on the biblical and experientially-confirmed paradox that the way to get the best out of Christians is less to tell them to be good and more to tell them they've been forgiven. Of course there are charlatans who go through the motions of being a Christian who will take advantage of this. But for people who have really been gripped by the Spirit, who really have been sensitized to the horror of their sin and the loveliness of their Savior, grace without demand produces people who meet the (non-optional) demands and conditions God places on us. NT authors continually and explicitly tie the present, everyday demands and problems and struggle of even mature Christians with the very first thing you learn as a Christian. (The OT does this too, actually, but that's for another post.)
I sometimes come across moving, bible-saturated exhortations for greater obedience, greater sacrifice, greater holines - exhortations which seem to arise out of frustration with mediocre Christians, and exhortations which quote selectively from Paul, only quoting his calls for obedience, and missing the way Paul (and Moses and David and Isaiah and Ezekiel and . . .) always rigorously contextualize such (non-optional) calls within God's grace which cleanses, which transforms, and which beautifies. Aim at grace, and you'll get obedience as well; aim solely at obedience, and you may get neither. I believe both the Scriptures and experience bear this out.