What is 'Grandfathering'?Edit
In short, grandfathering is taking some skills from your current class to another class, then back to the original class. This essentially grants you additional skill points within that class.
How can I grandfather some skills?Edit
First you need to level up your soul to Soul Rank 5. (This is separate from your character level and is account based.)
Next you need to decide which skills you want to bring over as part of the grandfathering process and then preform a class change. Then once you reach the desired level you class change back to the original class and simply leave the skills you transfered from the first class alone.
This allows you to have skills you might not be able to have early on at lvl 1. Then you can either save skill points to further invest in those skills when the appropriate level is reached or you can invest in other skills you are yet to access.