Surely, a guard is a need for the Patriots, but drafting one in the first round, especially at 21, is not necessary. You can find talented offensive linemen later on in the draft. For example, Michael Onwenu and Ted Karras were both 6th round picks.
Cordell Volson is the type of player that could be a gem found in round 3 or later of the draft.
Let's take a look:
Name: Cordell Volson
Position: T/G
School: North Dakota State
Size: 6'-6" 315lbs
40 time: 5.