The Book of Job (c. 500BC) in the Old Testament discusses this at great length. The "accuser" (Satan) says people only worship God because they get good reward

The Book of Job (c. 500BC) in the Old Testament discusses this at great length. The "accuser" (Satan) says people only worship God because they get good rewards. If God doesn't reward them, they'd stop worshipping. God disagrees, and allows Satan to test his theory by inflicting great suffering on a righteous, blameless person (Job). Job's friends say "obviously you've sinned, and this is punishment from God", which Job denies. Job eventually demands God justify his suffering, and God takes him on a walk through all creation, effectively saying "you'll never understand divine justice, because it's way too complicated". So this is not just a recent Christian question, but one that dates back to early Judaism.