Well it certainly "reads a code in them" in some fashion. or perhaps souls obscure the code, hence the need to remove so many of them.

Yeah, that part is quite unclear. The way it is phrased makes me think it is something along the lines of a calculation that is successively approximated. Each "flash" garners an inching toward the totality of the calculation. At the point of 144,000 the calculation can be finally be solved, having gained enough variables and the output being calculable.

Or perhaps it is the reverse. Each "code flash" gives a part of the

*answer* and when 144k survivors are left, it can calculate the correct 144-thousand variable equation for that "solution." Simple algebra really at that point, just solving for X (just 144,000 X, Y, Z's and so on).