The whole reduced to its load-bearing parts. A summary is a claim about what mattered.
Latin summarium (an abstract, a summing-up), from summa (the sum, the total), from summus (highest); a summary was always the highest points of an account, not a smaller copy of the whole of it.
The whole reduced to its load-bearing parts. A claim about what mattered, standing in place of everything that was left out.