Soteriology is eschatology, and that means soteriology  has to have an already/not yet structure.  Rejecting either justification by faith or judgment according to works breaks the bond of eschatology and soteriology.  Another way to say this is soteriology is about what happens in time .

The alternatives are:

1) Antinomian: We got saved; we’re in, and can do what we please between now and judgment day.  Already without not yet.  Time doesn’t matter at all.

2) Legalism: We’re not in at all, so we’ve got to dig in and do good works so we can impress Jesus at the last day.  Not yet without already.  Time seems to matter a lot here, but it’s my time that matters, not the time of Jesus.  For the legalist, Jesus didn’t do achieve much of anything in time, and He leaves it pretty much up to me.

Of course, judgment according to works doesn’t make much sense unless we also acknowledge the reality of apostasy.  But acknowledging apostasy is also an affirmation that soteriology is what happens in time.