Kings are the pieces that determine the fate of the game--you capture the king, you win. That's what "checkmate" is. A "check" is a stage before "checkmate". There may still be an opening for a king under "check" to escape and turn things around.

The trouble is, a king can only move one space on the board. Any direction, but only one space.

A bishop, on the other hand, is a powerful piece that is potentially second only to the queen. The queen can move in any direction for as far as she'd like. A bishop, however, moves only on the diagonal as far as he'd like.

Removing a bishop from play is removing a large safety net from the king.