To believe in religion is a hard pass, but to believe in Jesus, wholeheartedly yes.

 God in his foreknowledge has elected and predestined and ordained every human being to be saved and he did save them all at the cross yet positionally, meaning they have to receive what he's already done for them positionally at the cross by believing.

 You may very well be a theist but you still need to be Born Again in order to get into Heaven when you die.

God is faithful/sleepless to watch over His Word to perform it for the believer and not for the unbeliever or doubter or the one with little faith! 

 I do believe that there is a difference between "losing" your salvation and "walking away" from your salvation!

 Adam went from life to death and so did Lucifer and so can we if we don't guard our hearts with diligence which the Bible is very clear throughout the whole Bible, Old Testament and New Testament Saints

 All of us are born with the sin and death nature via procreation which is why we need to experience the New Birth via Regeneration and/or Recreation!