Why is the historical thinking skill of interpretation important for historians?

To develop a deeper understanding of the past by using sources.

By using this skill, the historian can analyze and evaluate secondary sources in order to fit it in a much larger context of bias, motivation, and other things that might have influenced that source, why, and what it says about that historical period. This skill is also the one used to understand some sorts of questions asked about the particular interpretations and even circumstances regarding the period, the happenings, and the context in which interpretations might be written about by historians.