Two on a raft have a better chance than if each clings to separate spar
is spoken by Mrs. Linde in Act III of the play. She is directing her conversation to Krogstad, a former lover whom she had to give up years ago. Krogstad is also the antagonist of the play who tries to sabotage Nora's comfortable and seemingly happy home life by threatening to expose the fact that he had once loaned her money; this action is considered a social faux pas which would deeply embarrass Helmer.
Since meeting again, Krogstad and Christine realize that they are both alone in the world. They once shared a deep love which, apparently, Krogstad still feels. Christine is also alone, but down on her luck, wishing to find "something" to invest her life on. This "something" is going back to Krogstad and try to make up for the past together.
It is at this point where Christine proposes reuniting again as a couple. Two lonely people can help each other go through life rather than taking in all of the sad circumstances alone. "Two in a raft" is an allegory to survival; the raft that carries two people will more likely get to shore. This means that, if they get together, they may be able to succeed at something. If they continue their separate personal issues, they will be more likely to implode and become lost even further.