The Absurdity of Prayer (Psalm 50 (LD 45)

Our catechism moves from the law of God that we obey out of gratitude to teaching us about prayer.  It does seem a bit strange that as Calvinists we would pray and that our confessional documents would have strong language regarding the necessity of prayer.  Why pray if everything is determined?  What can prayer do for us in our Christian life?  Do we pray to change the will of God or do we pray for another reason?

Choose Whom You Will Serve (Joshua 24:15)

Joshua gives the exhortation for Israel to choose whom they will serve.  The Lord is the one who has assured Israel that He chose them to dwell in the land that was promised to Abraham.  So, if the Lord has chosen this people then why must this people choose the Lord? This is a rather strange declaration, and what does this have to do with profession of faith?