How to understand the "synchronous" and "asynchronouns" messaging in JMS?

Like I understand this:

asynchronous - MessageListener: Use this on a server that listens to a queue. When a message arrives, then deal with it immediately. The server keeps listening to this queue.

synchronous - consumer.receive(1000): Use this on a client applications that now and then needs to check if a message is intend for this client. Example: poll every 60 seconds. This only opens a connection to the server shortly. The 1000 milliseconds will keep this connection open. If a message arrives within these 1000 milliseconds, then the message is consumed and the connection is closed.

If you understand it better like this, consumer.receive() uses a pull model: you read from a queue and are blocked waiting for this message until it comes, or some timeout has elapsed.

Using a listener uses a push model: you register a listener and, when a message comes in, the listener is called, in a separate thread.

Everything is done in a thread in Java, and the listener call is no exception. Whether the listener message handling prevents the processing of other messages in the queue depends on how many threads are dedicated to message processing. If you configure Spring to use a pool of 5 threads to process messages asynchronously, then 5 listeners will be able to process messages in parallel.