Enchanted creature gets +1/+1.
Sacrifice Briar Shield: Enchanted creature gets +3/+3 until end of turn.
4/1/2008 When you cast Briar Shield’s activated ability, Briar Shield is put into the graveyard as a cost. The +1/+1 effect immediately ends, but the +3/+3 effect won’t begin until the ability resolves. The enchanted creature gets no bonus while Briar Shield’s ability is on the stack. If its toughness is 0 during this time, it’ll be put into the graveyard.