The card originally known as Judgement Day derives from Christian scripture, but in most religions and cultures there is the concept of spiritual rebirth after the end of the world. This is another card of transition, like Death and the Tower, but its energy is neither violent nor catastrophic despite the fact that its power is far greater. This is the energy of creation without destruction, impossible on the material plane but certainly possible in the world of the spirit. There is rebirth not through discarding negativity, but through integration of all parts of the self. The spirit is cleansed and restored without loss or addition. It remains the same, but different.
Traditionally, Judgement Day is a day of reckoning, where you must answer for your actions and your inactions. The tie to Justice cannot be missed, and in a sense, Judgement is an elaboration on cause and effect, and on the notion of cosmic justice. In the light of Judgement the effects of your actions and inactions do not exact a toll or give a reward on the physical plane, but on the spiritual level. Where you have been determines where you are going, and what you have done plays a role in what you still must do. The cycle can never really end because the spirit never dies, but lies on in an eternal existence that we may never fully comprehend.
As the Judgement Day represents the union of the material and spiritual world into a single unit of manifestation, so too can Judgement show the union or reconciliation of the different parts of yourself. The three human figures found on most versions of the card allude to this. The man represents the renewal of the conscious mind, the woman is the rebirth of the subconscious, and the child is the boy from the Sun, the eternal child in us all. United into one voice, they praise the angel that appears in the sky. After the non-destructive cleansing and restoration of Judgement, matter, mind and spirit are one - now and forever.
The Rider-Waite symbolism is particularly interesting. In the background are the mountains that first appeared on the Fool. The ocean is the termination of the river that flows through the Major Arcana, starting with the Empress. Gabriel's banner is red on white, the same as the Magician's robes. As with everything in life, the beginning is woven irrevocably into the end and the end will eventually lead to a new beginning. At its core, Judgement is not a card of endings, but of beginnings. This journey is over but the next, a journey on a higher plane of existence, is approaching. Judgement is the preparation for that journey; the last stop before eternity.
Judgement's appearance in a reading often signals that a major change is heading your way, but unlike Death and the Tower, the change will not be a destructive one. The change is under your control, and in fact you can even turn your back on it if you wish. In time, however, you will likely regret doing so - this is another lesson of Judgement. Decisions such as the one it offers are necessary to growth and spiritual development, and you cannot run from them forever. The day of reckoning will come someday, and you will have to admit where you have gone wrong in order to receive rewards you deserve.
Judgement is also a card of cleansing, representing a time where your slate is wiped clean and you can start over, with all your debts taken care of and with nothing to worry about. This may seem too good to be true, and for a lot of people it is, because they ruin their new chance with thoughts of the mistakes they made in the past. Judgement teaches that while you must be aware of the past and the lessons you have learned, you must not degrade yourself because of mistakes - mistakes are just part of learning! Put the past behind you and look to the future, ready to begin again. Now is time for a definite step, so don't let the shadows of the past hold you back.