Locke wants them all dead by First Recruiter

I've read a lot of theories as to what Locke's motivations are with the candidates. I'm sticking with the fact that Locke wants to kill them all at the same time, possibly on the Ajira plane.

Others have argued if Locke just needs all the candidates dead, then why did he save a few of them earlier, like Kate, Sawyer and Jack. Locke's intentions are definitely sinister, but he needs to play nice until he gets all of his eggs in one basket. Locke and Jacob both have to keep adapting to the conditions of the game they're playing.

Locke was warned by a potentially young Jacob that he cannot kill Sawyer directly. So he goes with an indirect way and leads Sawyer down a ladder with a loose step. Notice that Locke checks the integrity of the ladder and then switches. When Sawyer gets to that spot, the step breaks, but Sawyer still held on. I believe this is when Locke's plan had to change. Maybe the candidates have protection from accidents too? Locke tried to kill Sawyer in the same way he did with Jack and Hurley, off a cliff. Sawyer was already "on his own", so if he died, nobody would know about it and Locke could move on. He realized that killing them one by one wouldn't do it, so he moved to plan B, killing them all when they're together.

A side note, Jacob also has to adapt to the conditions of the game. When he told Hurley to take Sayid to the temple he was contemplating. Two birds, one stone, get the candidates to a safe haven and fix Sayid. After Sayid got infected by the black water, Jacob was kneeling over the spring with a look of slight defeat, like he didn't expect it to happen. Jacob had to adapt again, but kill two birds with one stone. Get Jack and Hurley away from the place where Locke was about to invade, and restore Jack's faith at the lighthouse. But I digress...

The reason Locke saved Kate from getting stabbed by Claire is that he needs Kate in order to manipulate Sawyer and Jack. Locke needs everyone or else his plan won't work. At the end of "The Last Recruit", the candidates bailed on Locke, except for Jack. Since Jack came back he's the only recruit (except for maybe Sayid) that's with him, and Jack is Locke's only chance at gaining everyone's trust back. Once he gains their trust back, he can get all the candidates together and destroy them. Once the candidates are dead, he can just kill everyone else on the island by himself. This is unfortunate for Miles, Ben and Richard, even though Straume and Linus were on the list on candidates, perhaps it's there parents.

The MAIN reason why they all have to die together is because if there's only one candidate left on the island, then that person is the new Jacob and embodies all the same powers as Jacob. Then Locke will be back where he started, him and the candidate, stuck on the island, and he would have to wait a long time until more people arrive to manipulate into whacking the candidate.

Please and thank you!