If the republicans vote to repeal the bill, they have the votes. But, then they have to pass an ENTIRELY NEW bill, which they don't have the votes for, because the Democrats in the Senate can fillibuster, because a new bill requires 60 out of 100 votes. If the republicans repeal and then can't agree on a new bill, or get it passed, then the media will blame all the coming rising healthcare costs on them, when in fact, they were created by infation and obamacare.
So the republicans are trying to "revise" obamacare, which only requires 51 votes in the Senate (and almost passed last time). The problem with the "revise" strategy is that the neo-con conservatives like McCain, Graham, and McConnell want to put "lipstick on a pig" and not really change obamacare because, deep down, they want govt run healthcare. If they can pass "obamacare lite" as Rand Paul called it, then they get all the glory/headlines for being "conservative", meanwhile the revised bill is essentially the same.
I think Rand would like to repeal and replace but he knows it won't happen, so he's trying to play hardball so that the revised bill is as conservative as possible.