The runoff election will be comparable in many ways to the Democratic primary race between Barack Obama and Hillary Clinton at the start of the 2008 election season. Shelly Yachimovitch is comparable to Obama: She draws enthusiasm from young voters, has never held party leadership, and runs a social justice agenda. Amir Peretz is comparable to Hillary Clinton: a seasoned politician who runs the party line. Peretz led the Labor party between 2005 and 2007, and having served as Israel's Defense Minister during the Second Lebanon War in 2006.
Given that Israel votes using a closed list system, in which candidates are ranked prior to the election, the runoff will be a rare occasion for new blood in the upper echelons of the Israeli government. However, the two candidates who will drop out of the running, Amram Mitzna and Isaac Herzog, are also party regulars. It is likely that their constituencies would be more inclined to choose Peretz in the runoff.
The outcome of the runoff will have important implications for the political influence of the Israeli center-left. A more mobilized Labor party may be a tough constituency to keep inside the current Netanyahu government's coalition, especially considering its strong far right wing component. The burden would be greater should labor come under Yachimovitch leadership. Either way, the vote is a key test for the Israeli left as its constituents decide in what direction to take the Labor party.