How does article 2 relate to the oath of office?

Clause 8 of Article Two of the United States constitution states:

Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:-"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States."