What is the main contention of the presence of evil in relation to God's nature, as argued by Voltaire?

Voltaire's philosophical critique surrounding the existence of evil largely hinges on the relationship between God's nature and the presence of evil in the world. The main contention is that if God is omnibenevolent (all-good) and omnipotent (all-powerful), then the existence of evil creates a problem, often referred to as the problem of evil. Voltaire argues that if a perfectly good and all-powerful God exists, then there should not be any unnecessary evil or suffering present in the world.

This leads to the conclusion that the presence of evil is incompatible with the traditional understanding of God. Essentially, if evil exists, it raises doubts about the nature of God—either He is not all-good, not all-powerful, or He does not exist at all. This perspective invites a critical examination of theodicy, or the justification of God’s goodness despite the existence of evil. So, the assertion that if God exists, then evil cannot be present accurately captures Voltaire's argument about the challenge evil poses to the conception of an all-powerful, all-good deity.