Note that as of the release of FAQ 1.9, We Are Not Idle does not work as described here.
Gloin began to talk of the works of his people , telling Frodo about their great labours in Dale under the Mountain. "We have done well," he said. "But in metal-work we cannot rival our fathers, many of whose secrets are lost. We make good armour and keen swords, but we cannot again make mail or blade to match those that were made before the dragon came. Only in mining and building have we surpassed the old days. You should see the waterways of Dale, Frodo, and the fountains, and the pools! You should see the stone-paved roads of many colors! And the halls and cavernous streets under the earth with arches carved like trees; and the terraces and towers upon the Mountain's sides! Then you would see that we have not been idle." -- Gloin, The Fellowship of the Ring
Well, rather than mining for precious metals and building massive halls, this deck mines for resources and builds a swarm of dwarves. In general, the plan of this deck is to be playing dwarf allies for the first several turns while drawing cards due to the effects of Ori and Legacy of Durin. At some point, We Are Not Idle will clearly yield a sizable return with 8+ dwarf characters on the table, and after gaining a ton of resources we play as many dwarves as we can before readying them all with Lure of Moria. This could allow us to play 5+ allies in one turn! And so anytime we can do that with the combo we ought to do so. Of course they are all boosted in and by Dain Ironfoot while he is ready. In the mean time, Bombur can become a decent defender with Dwarven Shield, and maybe gain us resources too with his sizable hit pool.
When using A Very Good Tale, exhausting 5 cost worth of allies is usually enough to net you some more allies. Tome of Atanatar will let you recur the tale or either a Lure of Moria or We Are Not Idle if you need it to complete the combo. Song of Wisdom is played on Dain, but A Good Harvest can serve the same function. Both allow us an easier time of stacking resources on one hero and using them to play all the dwarves. Since most of the allies are or , we probably don't need Narvi's Belt. This can mean that Erebor Battle Master may or not see play, but that is usually okay since he can be overkill.
This deck definitely works, I've seen games where it had around 12 allies or so in play by turn 6. From the mid-game onward it always dominates the board state with an absurdly strong dwarf swarm. It is able to operate in solo, but it seems to work best when another deck can handle the early game for it so it can focus on building itself up to be unstoppable.