Question

Molarity material = density x 1000 x (%/100) x (1/molar mass material)

1000 indicates?

Answer 1

1000 is the volume of the solution.

Since you want M, that means you want mols solute/L solution.
1000 is volume of solution.
1000 mL x density in g/mL = grams solution.
1000 x g/mL x (%/100) = grams solute.
1000 x g/mL x (%/100) x (1/molar mass solute) = M where grams solute/molar mass solute = mols solute. So you now have mols solute/L solution and that is M.