Definition: The Block Gas Limit is the maximum cumulative amount of Gas that can be consumed by all transactions within a single block. It dictates the "capacity" of each block.
Core Logic:
Limited Capacity : Blocks aren't infinite. If the limit is 30 million Gas and each transfer costs 21,000 Gas, the block can only fit roughly 1,428 transactions.
Miner's Discretion : Miners act like bus drivers, prioritizing "passengers" who pay higher fees (Gas Price) while ensuring the total weight doesn't exceed the limit.
Network Security : The limit prevents blocks from becoming too large, ensuring that nodes can process data quickly and keeping the entire blockchain stable.