"Whoever is not against us is for us" is a very hard saying: it seems to conflict with another, similar statement in the Gospels (Luke 11:2); it is hard to reconcile with the sons of Sceva in Acts 19; it is complicated by Jesus' teachings about judging by fruits in Matthew 7; it is hard to know what "being against" even means. Zack reads these difficulties as an invitation away from systematic theology and towards increasing dependence on God's Holy Spirit. Moreover, he draws out important principles here with which we should reckon. Works, while not the basis of our salvation, reveal Christ-in-us. Our moment of hyper-Protestantism and church decline demands increasing ecumenism. Finally, perhaps most importantly, we must remain open to the new -- to God's surprising, scandalous work outside our own walls.