They did not appreciate God with His true appreciation.

[And they have not appraised God with His true appraisal.] The true appraisal of God and the glorification of Him with His true greatness are achieved through two things: The first is taking lessons and evidence of God's greatness from His signs in this vast universe. The second is believing in the Last Day and the great terrors it contains. We must strive to maintain these two things so that we may truly appreciate God and fear Him with the fear He deserves.