The reason we believe is because God predestinated us to be conformed to the image of his Son. Rom 8:28-30 To ensure that his people would be conformed to the image of Christ, God predestinated each one to that conformity to his Son.
28 And we know that all things work together for good to them that love God, to them who are the called according to his purpose.
29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
30 Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified. 13