We have often heard it said that the Number 13 brings bad luck, particularly when people gather in a group, and that we must never be 13 at table. Why? Because the Number 13, which is a living entity like all numbers, acknowledges and welcomes only those human beings who are truly pure. And because this number is also very active and dynamic, it can harm those who do not possess the feminine qualities of goodness, love and gentleness which counterbalance its influence. You must be pure and full of love in order to feel at ease with the Number 13. On the physical plane the Number 13 is linked to the cross (1 + 3 = 4), that is to say, to suffering, to prison.
The cross is a cube unfolded into two-dimensional space, and a cube represents limitations, or a prison. The Number 13 can therefore ‘bring bad luck’ as we say; but the misfortune does not come from the number itself, but from the particular manner in which each person receives its influence, according to his physical and psychic structure, or their degree of evolution. This explains why, in response to the Number 13, certain people fall ill or have accidents, others begin to reflect on things, while still others feel stimulated to act, and to act wisely.
Omraam Mikhael Aivanhov