What is the difference between que and de que in terms of que being a relative pronoun and de que being a conjunction. I see de que used in place of que all the time, but have no idea why. In terms of being understood does it matter using one instead of the other. I can find an example from the lessons if needed.

Here is an example: Son la personificación de que el esfuerzo da frutos. Why not: Son la personificacion que el esfuerzo da frutos.

de que el = of the que el = that the

Where did you get that? Is it in the lessons somewhere?

It's not in the lessons and I may be wrong. I put both sentences in a translator and that was the only difference in the translations. Of course, that could be only in this case, not always. Maybe someone else will have a better idea.

See if you can replace "that" with "which" in your sentence and if it still makes sense, use "que", otherwise use "de que". "de que" is a conjuction, meaning "of", while "que" is just a relative pronoun.