Why Christians Lack Assurance

The quote below is taken from "Why Christians Lack Assurance" by John MacArthur.

QUOTE
So some lack assurance due to strong preaching, strong conviction. Some lack assurance because of an inability to accept forgiveness. Some lack assurance because they fail to understand the rich truth of the gospel, the work of Christ. Some lack assurance because of an inability to remember the time of salvation. Some lack assurance because of the remaining power of their unredeemed flesh. Number six, some lack assurance because they don't see the hand of God in their trials.
UNQUOTE