Lumen, The Blessed City

Lumen , the Blessed City enters the battlefield
tapped.
{t} : Add {w/u} to your mana pool
Each time you gain life, untap Lumen the Blessed
City.
Emergency - When Lumen, the Blessed City
enters the battlefield, if you have 7 or less life, all creatures with Lifelink have instead Lifelink 2