[Python] Discord.py read messages from channels

I m trying to listen to all messages from specific channels inside guilds that i m not owner, i started to trying listen to all messages with the code below, without success. How can i do that if possible using the channel id?

Thank you!

import discord

client = discord.Client()
guild = discord.Guild
messages = []


print("Bot started")
@client.event
async def on_message(message):

msg = message.content

if msg != "" :

messages.append(msg)

while True:
print(messages)

client.run('TOKENHERE')

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