a).Paul uses the term darkness and light because the two elements are a total contrast,as is our transformation from being sinners to being committed Christian.
.He reminds them of where they come from because people tend to forget how bad things were. Forgetting the past can also lead to making the same mistakes again, returning to their basic sinful nature.
c). God accepts us for what we are, and while we may not be saints, Paul lets us know that we are all equal in Gods
eyes.
d). They are contrasted as being a place of darkness ( where satan dwells) and the kingdom of heaven which is God's kingdom of light and love.