For God so loved the world He gave His only begotten Son so that whosoever believes in Him should not perish, but have eternal life.
Sounds pretty clear to me.
“...whoever believes in Him...” is the key phrase here that you are making believe doesn’t mean what it means. If you do not MANIFEST your belief in Him it isn’t real. Period. Full stop. Christianity isn’t magic or incantation voodoo.
Clarify “MANIFEST your belife in Him”.