What Is the Relationship between the Block Reward and the Security Provided by the Longest Chain Rule?

The block reward, which includes the newly minted coins and transaction fees, is the primary economic incentive that drives miners to expend computational power (hash rate) to secure the network. The high hash rate, in turn, makes it prohibitively expensive for an attacker to create a longer, malicious chain to subvert the longest chain rule.

Therefore, the block reward directly funds the network's security, ensuring the integrity of the longest chain rule and preventing confirmed double-spending.