Just as the Magician introduces one to the Major Arcana or the Trumps of Tarot, the Aces of the deck introduce one to the Minor Arcana or the Pips.
The Four Aces are the pillars which support the house of the Minor Arcana. Each one is a Book in and of itself.
The Aces seen from the Hermetic perspective are the Virtues: To Will, To Dare, To Know and to Keep Silent. In practice they represent the four poles of the tetrapolar magnet.
To students of the Kabbalistic system the Aces symbolize the “so-called” name of God i.e. the law of cyclic manifestation or the Tetragrammton.
For most Tarot readers however the four Aces represent the four “magical” elements and/or the seasons of the solar year.