review matrix

Expand on the passage below and why a review matrix is important?

“matrix is a box or rectangle with rows and columns, like a spreadsheet. In a review matrix, the rows are for documents, such as journal articles, and the columns are for the topics you will use to summarize each of those documents. A summary of an article in a review matrix describes only the most pertinent points about the topic. Table 51 shows a generic example in which the first two rows are journal articles and the columns are the first four topics of the review matrix”.