Bonds of Faith has a variable effect depending on the creature type of the creature that it is enchanting.  When attached to a creature with the subtype of human, it will give this creature +2/+2.  When attached to a non-human creature, that creature will be unable to attack or block.

Some creature cards in Innistrad have the creature type of human and some other type. Bonds of Faith’s ability only cares if that creature has the type or human, being another type in addition will not remove the +2/+2 or cause it to be unable to attack or block. For example, Mayor of Avabruck has the creature types of Human Advisor Werewolf. A Bonds of Faith attached to it will grant this creature +2/+2 and not prevent it from attacking or blocking. However, when transformed into Howlpack Alpha this permanent will just have the creature type of werewolf. As it is transformed, this same Bonds of Faith will prevent this creature from attacking or blocking and not give it +2/+2.