Bad pass blocking can neuter even the most talented of offenses; when offensive linemen consistently can't sustain their blocks in pass protection or let opposing rushers slip through, the whole offense suffers. Wide receivers don't have the time to get downfield, preventing them from making big plays and eliminating the possibility of double moves. Running backs and tight ends that would be safety valves or mismatch opportunities have to stay in and block instead, allowing the defense to focus more of their attention on fewer receivers. Oh, and the quarterback doesn't have much fun, either. This paragraph can be used in full to describe the offense of the 2009 Chicago Bears.
You don't have to be a Bears fan to know that offensive linemen are hugely important, though. Some things are impossible to quantify when it comes to offensive line play, but one thing we track at Football Outsiders is "blown blocks," those plays in which an offensive lineman is responsible for a quarterback hurry or a sack. These numbers are inexact, but represent a decent approximation of how many sacks or near-sacks a player was responsible for over the course of a given season.
In 2009, the offensive line that allowed the most sacks was also the one that went through the most players. The Buffalo Bills had 11 different players start at least one game up front for them on offense, and those linemen combined for a league-high 28.5 blown blocks leading to sacks. In addition, running back Fred Jackson led all backs with four blown blocks that led to sacks.