Evangelizing as a church activity
And Paul, as his manner was, went in unto them, and three sabbath days reasoned with them out of the scriptures
And he reasoned in the synagogue every sabbath, and persuaded the Jews and the Greeks.
Paul spreads the Gospel to the Jews first and then to the Gentiles.
Visiting the sick and praying for them
...Wherefore it is lawful to do well on the sabbath days.
Jesus in this verse gives us a very good example of how you should spend your time at church. It is not by boring yourself to death but by doing something good on that day. Jesus endorses the idea of evangelizing, going to see and pray for sick people (Pharisees did not allow such activities as seen in Matthew 12:10) and all other activities beneficial to mankind.
Church activities must be to the glory of God
If thou turn away thy foot from the sabbath, from doing thy pleasure on my holy day; and call the sabbath a delight, the holy of the LORD, honourable; and shalt honour him, not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words:
These activities we do must not be self centered. We must think of God and how these activities will affect the Gospel work.
Note: All verses indicated come from the King James Version