This is the lowest level at which you get a daily quota of votes to spend on other monks' nodes. With each new level you attain, this quota increases. Details at Voting/Experience System.
(If you happen to lose enough XP to take you back down to Level 1: Initiate, and you still have some unspent votes, don't worry — unused votes never get taken away.)
Note also that at this level (actually, all levels 1 through 5), you get an XP bonus for spending your entire daily vote quota.
Level 2 is also the minimum level at which you get to see the Worst Nodes listings.
See also: I just became a Novice; Why can't I vote yet?