When this creature enters, you may
sacrificeTo sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. A player can’t sacrifice something that isn’t a permanent, or something that’s a permanent they don’t control. Sacrificing a permanent doesn’t destroy it, so regeneration or other effects that replace destruction can’t affect this action. (CR 701.21) a land. If you do, draw a card.
ThresholdAn ability word has no rules meaning of its own. It groups abilities with similar themes; the text following it explains this card’s effect. (CR 207.2c) — As long as there are seven or more cards in your graveyard, this creature gets +1/+1 and has
vigilanceVigilance is a static ability that modifies the rules for the declare attackers step.
Attacking doesn’t cause creatures with vigilance to tap. (See rule 508, “Declare Attackers Step.”)
Multiple instances of vigilance on the same creature are redundant. (CR 702.20).