Mono-White Aggro floods the board with efficient creatures like Fortress Kin-Guard and Search Party Captain, so you need both a way to remove a key blocker or attacker and a way to protect your own clock. Journey to Nowhere exiles their best threat, such as a buffed Leonardo, Big Brother, clearing the way for your hexproof creatures to keep attacking. Mask of Law and Grace grants protection from red, which doesn't help here, but it still grants protection from black, which is irrelevant against this all-white opponent; its real value is minor since the opponent has almost no black or red removal to dodge, so only bring it in as a cheap Ancestral Mask and Ethereal Armor booster rather than for its protection text. This is a race matchup overall, so keep Armadillo Cloak and Ancestral Mask in to out-damage their go-wide plan.