Called to Worship (Psalm 40; Hebrews 10:5-7)

The Lord calls us to worship and to make the Lord our focal place.  When we are called to worship as a people what is the basis of the Lord calling us to worship?  How are we called out of the world to Worship our God and our King?

Exhorted to Worship (Hebrews 10:25)

The people who receive the message from Hebrews seem to be struggling to keep their faith.  The author in Hebrews exhorts them to keep their faith.  Why would they want to keep their faith?  What does worship have to do with them keeping their faith?  How can such an old exhortation still be relevant today?