The judicial branch is not necessarily weaker than the other branches because Hamilton called it "the least dangerous branch." Perhaps Hamilton felt it is the least dangerous of the three branches of government because it does not make the laws as the legislative branch does; it simply interprets the laws that have been passed by the legislative branch and that have been approved by the executive branch.
Dangers enter into the law-making process because congressmen can be pressured by their constituents, lobbyists, and powerful people to write laws or vote for laws that are against the dictates of their consciences. Or they may wish to include in bills things that will enable them or their constituents. At any rate, there may seem to be more opportunities for corruption in both the legislative branch and the executive branch in lawmaking than in the judicial branch's interpretation of these laws.
The legislative branch is designed to manage conflict over interpretation, application, or enforcement of laws whereas the legislative branch can be embroiled with such conflict--a more dangerous situation.