What motivated early American lawmakers to organize the legal system on almost two parallel systems?

The motivation for American lawmakers to organize the legal system on almost two parallel systems was to ensure a system of checks and balances would be maintained. In order to constantly keep a system that checked itself, the legislative - House of Representatives and Senate, and the executive branch - the office of the President. The judicial branch is not supposed to be a branch that relies on political motivations, but rather passes judgement based on precedent and the decisions made by the executive and legislative branch.