The purpose of using rods, cubes, or tally marks in teaching numbers is to provide concrete representations of abstract numerical concepts. They make numbers less abstract. Numbers are abstract ideas. Using physical objects allows children to see, touch, and manipulate quantities, making the concept of a number more tangible and understandable. This is the fundamental reason for using manipulatives. The other options describe specific actions or benefits, but not the primary, overarching purpose. While children do count these objects and tally marks can aid in skip counting, these actions serve the larger goal of making numbers less abstract. The most accurate statement is that they make numbers less abstract. The final answer is $\boxed{\text{They make numbers less abstract.}}$