Why is an Entered Apprentice called an Entered Apprentice?

Initiation into the First Degree represents the candidate's symbolic entry into his heritage as an Entered Apprentice, where he receives the initial instructions of his Masonic journey 1. An article on the Grand Lodge of India's website explains that this entry signifies the beginning of a builder's effort to construct an ideal temple of character within himself, transitioning from a merely natural state towards a higher standard.

The United Grand Lodge of England records that pure Antient Masonry consists of three degrees, beginning with the Entered Apprentice, a stage meant to remind members that all are equal and have a duty to assist others. During this degree, the candidate is set to work upon the rough ashlar—representing the uncultivated mind—using working tools such as the twenty-four inch gauge and common gavel to pare away unnecessary rough edges and reveal the inner perfection 1.

The supplied sources describe this entry as a symbolic and moral beginning, though they do not give the historical or etymological origin of how the term "entered" came to be applied to apprentices in the early operative lodge records.