If Leyline of Sanctity is in your opening hand, you may begin the game with it on the battlefield.
You have hexproof. (You can't be the target of spells or abilities your opponents control.)
6/8/2016 A player’s “opening hand” is the hand of cards the player has after all players have taken mulligans and “scryed” if applicable. If players have any cards in hand that allow actions to be taken with them from a player’s opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.