This argument, albeit weak, states that the existence of God is required to bring justice into the world and to redress the injustices of the world in the hereafter.
Russell argues that if one takes a probalistic approach and views the amount of injustice in this world, then one is led to expect at least the same amount of injustice in the hereafter. Therefore, the concept of God serves no purpose.
First of all, it is incorrect to say that there is only injustice in the world. People tend to forget the justice in their favor or the injustice they commit, but remember the injustice against them. Secondly, one cannot plausibly conclude that there should be the same amount of injustice in the hereafter by considering the world and the hereafter to be parts of a same probabalistic system. If they were the part of a same system, then there would be no difference between them and one would not be able to call them distinctly. This is because for any thing that one finds in this world, one would expect it to occur in same frequency or intensity in the other world, and hence the two would be isomorphic. His argument appears to follow the following trend, if I see a crime being committed in front of me and the criminal is not apprehended, I should conclude that there is no police department.