What is the significance of the Masonic apron in rituals?

The apron is presented to the initiate at the earliest stage of his progress as his first gift, emblem, and tangible evidence of admission into the Fraternity 1. Made of unspotted white lambskin, its primary symbolic meaning is innocence, reminding the Mason of the purity of life and rectitude of conduct required to gain admission to the Celestial Lodge 1. Though its decorative details change as a Mason advances through the degrees, the fundamental substance of the apron remains the badge of a Mason throughout his career 1.

Historically, this rite of investiture is considered an ancient practice, paralleled by symbolic garments such as sacred girdles, sashes, robes, or shields used as badges of distinction across many ancient cultures and mysteries 1.

Masonic writers interpret the specific features and progression of the apron symbolically:

In the First Degree, the plain white apron represents initial purity of soul 2. Worn with the triangular flap raised over the quadrangular body, it symbolizes the combination of soul and body, making seven—the number representing the full constitution of man 2. Walter Leslie Wilmshurst takes the physical human body itself to be the true "badge of innocence" that the physical apron signifies 2.

In the Second Degree, the addition of pale blue rosettes indicates progress in spiritual growth and devotion to spiritual concerns 2.

In the Third Degree, additional blue ornamentation, silver tassels, and a silver serpent clasp represent advanced spiritual progress, the transmuting of base metals into spiritual riches, and Divine Wisdom binding the soul's vesture 2.

While regulations in some jurisdictions permit blue edgings, rosettes, or silver tassels to denote degree status or universal friendship, ancient practice favoured a plain, unornamented lambskin, viewing modern additions of paint, silk, or embroidery as unnecessary departures from its original simplicity 1.