The idea of soul parents originates in Egyptian paganism as the deity that breathes life into your soul. However, I don't know at what point it got added to the religion, and I almost never hear Egyptian pagans talk about finding their soul parents so I don't think it has a lot of importance in regards to who you worship. The concept has left that religion and can be found in New Age-leaning groups; it's now defined as the deity that creates your soul. Some people really cling to the idea that because they made your soul they're kind of a guardian angel-type figure: They've protected you all your life and know you better than any other deity, so it makes sense that they should be the main deity you worship! Thus they push for people to find their soul parent deity as that will be the best possible relationship with the Divine they can have.

Other people believe in the concept, but then say that other deities can be Something Else and that overrides the soul parent or can be added to them. For example, one blog I read from an Egyptian pagan talks about having a shrine to their spiritual parents, but then they also have "Beloveds", which they define as deities who have taken interest in you (and seem to be patron deities as we usually think of them).

As with all New Age concepts, it's quite flexible and many people have different, often contradictory views on how exactly this works. Hell, I even found differing accounts as to how many soul parents you can have.

There's not a lot out on there on this concept, but this is the general gist I got. I'm not sure how widespread it is in New Age groups, but it definitely pops up every once in a while.