From Talking Points Memo:
The Republican leader's decision is a major blow to the push by Cruz and powerful conservative activist groups, who wanted Republicans to unite and filibuster a continuing resolution until Democrats caved agreed to gut funding for the Affordable Care Act.
The decision clears a path for Democrats to pass a continuing resolution that funds Obamacare. Procedurally, Democrats need 60 votes (they have 54 members) to advance the House-passed continuing resolution. But Senate Majority Leader Harry Reid (D-NV) can strike the language defunding Obamacare with 51 votes, which frees up McConnell and every other Republican to vote against such an amendment. This way he never has to actually vote to fund Obamacare but doesn't force a shutdown over an unachievable goal.