Why does God save some and let others die ? In the garden of Eden some 6,000 years ago, an issue was raised regarding God's rulership. When a "serpent" asked Eve: "Did God really say that you must not eat from every tree of the garden ?", he challenged God's right to rule and way of ruling, whether it is just.(Gen 3:1)
Eve responded by telling the "serpent" that both her and her husband were allowed to eat from any tree in the garden except the "tree of knowledge of good and bad" that would bring death.(Gen 3:2, 3) Now the "serpent" replies: "You certainly will not die" if she eats from the "tree of knowledge of good and bad".(Gen 3:4) He thus told the first lie.(see John 8:44 regarding Jesus calling Satan "the father of the lie")
Next, the "serpent" convinces Eve that "God knows that in the very day you eat from it, your eyes will be opened and you will be like God, knowing good and bad".(Gen 3:5) Eve was seduced by the "serpent" with the thought of being "like God" and takes fruit from the "tree of knowledge of good and bad". (1 Tim 2:14) The "serpent" is later revealed as Satan (meaning "resistor") the Devil (meaning "slanderer").(Rev 12:9)
As a result of the rebellion in the garden of Eden, God's right to rule was challenged by Satan, his universal sovereignty. In order to prove Satan's contention that his rulership would be better, our Maker, Jehovah God, turned over the ruling reigns of the "world" to Satan then and there, until the end of the "last days" or at the finality of the "harvest" when Satan's reign will end.(Matt 13:30; 2 Tim 3:1)
What has been the consequences of Satan's rule over mankind for the past 6,000 years ? Suffering and death. In order to prove Satan's rulership as deeply flawed, God has allowed suffering and death to come upon his servants as well. In the Bible book of Proverbs, Jehovah says: "Be wise, my son (those loyal to Jehovah), and make my heart rejoice, so that I can make a reply to him (Satan) who taunts me."(Prov 27:11)
God's loyal servants are always "under the microscope" by Satan, testing them to see if they will renounce their loyalty to God. Hence, some suffer extensively and some die who maintain their integrity. For example, because of Jehovah's permission for Satan to bring upon Job serious afflictions, Job suffered extremely, losing all his children and business and later being struck with a loathsome disease that caused "painful boils", in which his wife said to "curse God and die".(Job c

1& 2)
At Revelation 2, Jesus said to loyal ones in Smyra: "Do not be afraid of the things you are about to suffer. Look! The Devil will keep on throwing some of you into prison so that you may be fully put to the test, and you will have tribulation for ten days (the number ten represents earthly completeness [such as the ten plagues or "ten words"], thus "ten days" would be their life on earth until death). Prove yourself faithful even to death, and I will give you the crown of life."(Rev 2:10)
Among the "world" of mankind, he allows Satan to do as he wishes, bringing great "woes" upon the earth.(Rev 12:12) And God permits suffering and death upon his loyal servants to prove Satan's claim false that he can put extreme pressure on them and cause them to capitulate in their love for Jehovah, just as he tried to do with regard Job.(Job 2:4, 5)
Satan is especially enraged with the "woman's offspring", the ones chosen by God for the "heavenly calling".(Heb 3:1), waging war with those "who observe the commandments of God and have the work of bearing witness concerning Jesus."(Rev 12:17)
Therefore, God has permitted suffering and death even for his loyal ones, to prove Satan's assertion that his rulership over mankind can bring happiness, is a lie.(see Luke 4:6, whereby Satan admits to Jesus that rulership of mankind was "handed over to me".)
However, soon, Satan's rulership over the "world" will end, for the "world" of mankind, those alienated from Jehovah because of having an independent spirit and loveless conduct (see Matt 24:12), will be annihilated at Armageddon.(Rev 16:14, 16)
Then Satan will be bound for "a thousand years" while the earth is transformed into a paradise, as God originally purposed when he placed Adam and Eve in the garden of Eden.(see Luke 23:43 regarding Jesus words to the evil-doer, that he will be resurrected to a paradise to be given the opportunity to live forever on it)
At that time, after the decimation of Satan and his co-horts following his release from the "abyss"(Rev 20:7-10), the issue of universal sovereignty or God's right to rule will have been settled once and for all, proving that Satan's reign over the "world" was a dismal failure and Jehovah's rulership is the very best. Then, there will be no more suffering and death on earth. Rather, "the meek will possess the earth, and they will find exquisite delight in the abundance of peace....forever."(Ps 37:11, 29)