What Is the Efficiency Gain of Using a Merkle Tree over Hashing the Entire Block Data?

Hashing the entire block data requires a full download and computation for verification, which is resource-intensive. A Merkle Tree allows for verification of a single transaction's inclusion with logarithmic complexity, O(log n), where n is the number of transactions.

This means verification time grows very slowly with block size, enabling fast, lightweight verification by light clients without sacrificing security.