We come together on Sundays to worship God, that is, to give to Him our praise, thanks, affection and more. That sounds right. So, how is listening to a sermon an act of worship? We're receiving, not giving. Some churches sense this. So, the first part of what they do on Sundays is called 'worship'. That's when everyone sings. That's when they give to Him their praise, thanks and affection. Then, once worship is over, there is the time for 'teaching'. That's the time when someone preaches a sermon. And that seems to make sense - but it leaves out an aspect of preaching that is so very important.
Let's go back in the history of the Church, back to when Israel just escaped from Egypt. Moses goes up to the top of Mt. Sinai and receives a message from God for the people waiting at the bottom of the mountain.
So Moses came and called the elders of the people and set before them all these words that the Lord had commanded him. All the people answered together and said, “All that the Lord has spoken we will do.” And Moses reported the words of the people to the Lord. (Exodus 19.7-8)
What happened? Moses told them the message from God and the people responded by submitting their minds, wills and affections to Him.
All that the Lord has spoken we will do.
That goes a long way to explaining what listening to a sermon is to be. So, to return to an example that I have used before, imagine that I preach a sermon about God's command, 'Husbands love your wives'. The response of the husbands should be,
All that the Lord has spoken we will do.
(And the response of the wives should be to learn how to depend on their husbands to love them.)
He is our Lord, and we are here to serve Him. So, we are to listen to a sermon with the mind, will and affections in submission to God. That's how listening to a sermon is worship.