The order of transactions and blocks is crucial to maintaining the integrity of the blockchain. By using hash functions like SHA-256, nodes on the network can verify the order of transactions and blocks, ensuring that:

1. _Chronological order_: Transactions and blocks are added to the blockchain in the correct chronological order, preventing tampering and ensuring the integrity of the blockchain.

2. _Causal order_: The order of transactions and blocks is consistent with the causal relationships between them, ensuring that the blockchain reflects the correct sequence of events.

3. _Consistent state_: The order of transactions and blocks ensures that the blockchain remains in a consistent state, preventing contradictions and ensuring that the blockchain is a single, trusted source of truth.

By ensuring the correct order of transactions and blocks, hash functions like SHA-256 help to:

1. _Prevent double-spending_: Ensuring that the same transaction cannot be spent twice, preventing fraud and maintaining the integrity of the blockchain.

2. _Prevent replay attacks_: Ensuring that transactions are not replayed or reused, preventing fraud and maintaining the integrity of the blockchain.

3. _Maintain the blockchain's immutability_: Ensuring that once a block is added to the blockchain, it cannot be altered or removed, maintaining the blockchain's immutability and ensuring the integrity of the blockchain.

By ensuring the correct order of transactions and blocks, hash functions like SHA-256 play a vital role in maintaining the integrity and security of the blockchain.