Question: What does it mean? After all, the flow of seed is meant for fertilization and birth.
Answer: In this case, a man doesn’t use his seed to fertilize a woman, which means that Zeir Anpin and Malchut don’t connect, and so the desire is used incorrectly.
A desire that is ready to be used in order to receive the Light in order to bestow is called a woman. If he and she work in order to bestow, a third element is created between them called a baby, which is their next level.
However, if she is not ready for that—if she is impure for example or if she is not intended to be a woman—it means that his seed is spilled on the ground. This means that it is a desire that is not ready at all and is, therefore, impure.
The spiritual system is very rigid. Your lower level is always below you, but when Light comes out of you to the lower level and it is not ready to be in contact with you for some reason, then it is your corruption since you haven’t defined the flaw, haven’t prepared, and haven’t discovered the flow as an upper level with regard to the lower.
Therefore, you must be purified by being bathed in the Light of Bina by connecting to the upper level. A man is Zeir Anpin, and the highest level is Bina. Zeir Anpin must be purified by the Light of Bina (the Light of Hassadim, bestowal), and he cannot work on that same day with the Light that illuminates now.
In addition, we distinguish between the different times of day and different days in the contact between a man and a woman: the weekdays, Sabbath, the beginning of a month, and so forth. It is an interesting dependency that is made of very rigid laws that determine when it is possible to work with the Light by conveying it from the top down.
From KabTV’s “Secrets of the Eternal Book” 3/5/14