Hi there,
in scripture I find numerous instances where God Himself adds to original scripture and corrects what people had up to then thought of Him and of His will. For example, David was big on fighting and battling with his enemies, but Solomo was considered wiser because God Himself commends him for not asking for the death of his enemies when God allows Solomo his wishes in the nightly dream. Later on certain prophets of God speak out loudly against animal sacrifices that up to then the jews had considered to be very important to their ledger of religious duties. Then Jesus appears and ends all sacrififices and his apostle Paul explains how the OT law was now gone and abolished and replaced by much gentler and more reasonable and altogether saner instructions. For example, instead of sacrificing bulls and oxen as a sacrifice of duty, we can now build a church or donate a good some of money to a hospital.
In the way we can see here a progression in scripture where God Himself corrects what others believed beforehand, we can also assume a progression in our view of God and of His will Himself. What started out as a feast of anger against man and of war and bloodshed, became a festival of peace, hope and joy, and God Himself was seen less as a figurehead of authority but more as the summit of virtue, goodness, life and love. In this I think we can say that eternal salvation of all people becomes a must. This is not against what the apostles believed as they only highlighted Jesus and His cross and the cross counts for all the world. And faith is not only possible for the living but also for the dead, so the deceased atheists and muslims will go to God and believe in Him and become free like us in Jesus Christ too. And that should be the will of a God who is love - because a God of love cannot inflict things like hellfire punishments, particularly as scripture says hell itself shall be destroyed.
God bless you!