My own summary description of "the Atonement" is that the Atonement is what gives repentance real meaning. To explain:
"To repent" means "to change" - and there would be no reason to strive to change if there was no difference eternally in the outcome. To me, the phrase "having a form of godliness but denying the power thereof" points directly to the heart of repentance and the Atonement - that the "power of godliness" is the ability to take us and make us into "more than us" - to allow the change for which we strive but never fully master to be actualized in the end - to give us the hope that our efforts to change will have an eternal impact.
So, to me, the "Atonement" covers the entire span of eternity (as far as it concerns us). It is the foundation of the eternal stages of life that take us from what we were and are to what we may become. It is God's governing grace that allows the process of eternal progression to occur.
WITHIN the Atonement, our part is repentance - a conscious effort to participate actively in the process of eternal growth.
That's why "easy grace" (don't worry about what you do; God will save you regardless) is so abhorrent to me. I don't believe we "earn" or "deserve" a reward, but I do believe we have to participate in the effort to grow - that we have to strive to change and become - that we have to "repent". I don't believe we will change totally and completely in this life, but I believe we have to be involved in the effort to become more than we currently are - and to "endure to the end" in that process.