The Catechism in Questions & Answers

682. What are the consequences of not attending the divine services?

Those who thoughtlessly neglect the divine services lose out on the blessing, grace, and powers contained in the word of God and in Holy Communion. Those who frequently abstain from attending the divine services without compelling reasons run the risk that their faith will diminish and their longing for the word of God will fade.
It is a sin to consciously reject or despise the divine service and the grace of God.