Overall meaning : The Almighty directs the believers to fear Him by doing what He commands and avoiding what He forbids and to seek His nearness and to fight for His cause so that they may achieve success by being saved from what they fear, gaining what they aspire to and attaining eternal happiness.
Then He states that even if the unbelievers possessed all that is on earth and twice as much again and offered it as a ransom to save themselves from the punishment of the hereafter, He will not accept it from them, and that they will receive a painful punishment. They will want to get out of the Fire after having been cast into it, but they will never get out of it, and they will suffer an everlasting punishment.