Google Pub/Sub pull method restart express server after every 1 min - node.js

Question

I am using pun/sub to pull messages when someone buys a subscription from google play.
const { PubSub } = require('#google-cloud/pubsub');
const grpc = require('grpc');
// Instantiates a client
const pubSubClient = new PubSub({ grpc });
const pubsub = () => {
const projectId = process.env.GOOGLE_PUB_SUB_PROJECT_ID; // Your Google Cloud Platform project ID
const subscriptionName = process.env.GOOGLE_PUB_SUB_SUBSCRIBER_NAME; // Name of our subscription
const timeout = 60;
const maxInProgress = 10;
const subscriberOptions = {
flowControl: {
maxMessages: maxInProgress,
},
};
// Get our created subscription
const subscriptionPub = pubSubClient.subscription(subscriptionName, subscriberOptions);
console.log(`subscription ${subscriptionPub.name} found.`);
// Create an event handler to handle messages
let messageCount = 0;
// Create an event handler to handle messages
const messageHandler = message => {
console.log(`Received message: ${message.id}`);
console.log(`Data: ${message.data}`);
console.log(`Attributes: ${JSON.stringify(message.attributes)}`);
//todo: you can update your backend here using the purchase token
messageCount += 1;
// "Ack" (acknowledge receipt of) the message
message.ack();
};
// Create an event handler to handle errors
const errorHandler = function (error) {
console.log(`GOOGLE PUB SUB ERROR: ${error}`);
throw error;
};
// Listen for new messages/errors until timeout is hit
subscriptionPub.on('message', messageHandler);
subscriptionPub.on('error', errorHandler);
setTimeout(() => {
subscriptionPub.removeListener('message', messageHandler);
subscriptionPub.removeListener('error', errorHandler);
console.log(`${messageCount} message(s) received.`);
}, timeout * 1000);
};
module.exports = pubsub;
And above file is called in the main.js file and every 1 min I am receiving log subscription ${subscriptionPub.name} found.
also, I have commented setTimeout code as of now but I want to understand why removeListener is important to remove the listener every one minute.