The Lord's Day

The first day of the week is the Lord's Day. It is a Christian institution for regular observance. It commemorates the resurrection of Christ from the dead and should include exercises of worship and spiritual devotion, both public and private.

On the first day of the week, when the disciples were gathered together to break bread, Paul talked with them, intending to depart on the next day, and continued his speech until midnight.
— Acts 20:7 (WEB)

Note

Sunday — the first day, commemorating the resurrection — is the historic Christian day of worship for Baptists, distinct from Adventist seventh-day observance.

Bible references

Exodus 20:8-11 · Matthew 12:1-12 · Matthew 28:1ff · Mark 2:27-28 · Mark 16:1-7 · Luke 24:1-3,33-36 · John 4:21-24 · John 20:1,19-28 · Acts 20:7 · Romans 14:5-10 · 1 Corinthians 16:1-2 · Colossians 2:16 · Colossians 3:16 · Revelation 1:10