Pacifism effects (MTG lingo for auras that don't allow the enchanted creature to attack or block ) are fairly common in Limited formats but not too useful in Constructed since they often allow the enchanted creature to use its activated, triggered, or static abilities
Declare blockers : the defending player chooses which, if any, attacking creatures s/he wishes to block
For the nostalgic among us, many cards also feature with the retro frame treatment
Instead of the temporary buffs that Prowess provides, your equipped creature gets +1/+1 counters
The card sees extensive play in Modern, Legacy, and even Vintage, where its status as a free counterspell makes it indispensable for most blue lists
Its purpose is to welcome you to the booster