(1) they espouse countercultural pacifism, and
(2) they draw deeply from the book of Revelation
This may come as a surprise to some critics of pacifism. Isn't the Revelation of John one of the most violent books of the Bible? Why do some pacifists emphasize it so much then? Isn't that counter productive? It's certainly counter intuitive!
Different streams of nonviolent Christianity
The answer comes in discerning between different streams of pacifism. Just as pro-military Christianity may be differentiated into "just war", "blank check" and other streams according to the degree they rely on secular wisdom, so anti-military Christianity may be differentiated into "absolutist", "apocalyptic" and other streams according to the degree they rely on universal principals.
Absolute pacifism, more typical of liberals, tends to gloss over the authority of the Old Testament in its search for a universal ethic applicable to everyone, everywhere, everywhen. Apocalyptic pacifism, more typical of Anabaptists, takes a different route, emphasizing the covenant transforming revelation (Greek: apocalypse) of Jesus. Absolute pacifism espouses timeless teaching, apocalyptic pacifism espouses time asymmetric, kingdom coming teaching.
Taking this route, an apocalyptic pacifist may: acknowledge God as warrior, whilst celebrating the resurrection of the crucified messiah as the climax of the eschatological war (Col2:15); acknowledge God as judge, whilst reserving judgment as a divine prerogative (Romans 12:19); acknowledge the Old Testament as revelation, whilst relativising it's applicability for discipleship now, not only for ritual but also for lifestyle. Rather than avoiding the Old Testament as absolute pacifists might, apocalyptic pacifists will highlight the foreshadowing of nonviolent messianic ethics in the Old Testament, such as the refusal of David to assassinate Saul qua Romans 13.
The book of Revelation
Turning to the book of Revelation itself, an apocalyptic pacifist would draw attention to the beautiful vision of the New Jerusalem, the contrasting vision of Babylon, with a call to live the future in the now (Matt 5), and a warning about Christendom as an expression of the latter. Apocalyptic pacifists do not see their ethic as being for everyone as an absolute pacifist might, but only for those called to live in countercultural witness against Babylon. They have much less concern for developing an ethic that everyone can keep, particularly in a society as pluralistic as ours.
Finally, apocalyptic pacifists draw attention to the paradoxical identity of Jesus as lion/lamb (hence Yoder's book title), and the revelation of warring empires falling, not by swords in the hands of many, but a sword in the mouth of one (Rev 19:21). Those who live by the sword will die by the sword. War has it's own karma. The lamb wins with a word. Militarism is renounced by apocalyptic pacifists, not because it is intrinsically sinful, but because it is rendered faithless given the revelation we now have.
Grace and apocalyptic lifestyle
Which brings us to the subject of grace. The radical reformers differed from the rest, not because they denied the salvation by grace, but because they decryed the slicing of salvation from ethics and God's grace from enemy love. Contra Luther, they affirmed James as an epistle of substance, not straw. Given we are saved by grace we are now called to engage our enemies, not just legally and justly, but graciously and lovingly (John 1:17) And so I appeal too, that we would lay down our swords and pick up our cross.