The word innumerable has many implications when compared to the fallen angels in hell. The idea that there are an uncountable number of angels refers to the story of the individual in the book of Luke. In Luke 12:6, God is to have said that even the sparrows are counted and loved, each one. The concept of the individual is that God loves each one of us separately down to the last hair on our heads. Milton uses this term to describe the severity of the angels falling. They are no longer in God's grace, God however does still rule them. The vastness conveys the idea that they don't belong anywhere, not even hell.