This is a good question, and you can start guessing what "abstract ideas" might mean by the context of the sentence; in the sentence guiding your question, abstract ideas is paired with "theoretical arguments." So, you can immediately tell that the two are similar enough to be paired together.
Oftentimes we make a division between theory and practice, or abstract and material. So, if practice is the actual doing of something, theory, we could say, explains the practice. For example, if you swing a bat and miss a ball, you just earned a strike. That's practice. Theory is the explanation of, say, why a curveball going so many miles per hour is a ball that you missed based on the angle of your bat and how fast you swung the bat.
Abstract ideas are similar--but not the same--as the theoretical. Think of a material object that you can hold in your hand. That object has very particular things about it. It has a certain weight, it exists in a certain space, and during a certain time. Abstract ideas don't have those qualities--they are not particular to any time or space. They cannot be held, or weighed, or measured like physical objects can be. For example, the idea of something that is courageous is not the same as a courageous act. A courageous act might be telling someone to stop bullying. That's the practice of doing something courageous. The abstract idea, though, is what "courage" is in the first place. "Courage" itself doesn't have a weight, measurement, or temporal or spatial existence.
I hope this helps.