What is the purpose of the Old Testament if we are only to follow the rules set out in the New Testament? Well, every single page in the Old Testament speaks of Jesus Christ. For there are hundreds of fulfilled Messianic prophecies, Messianic end times prophecies, typifications of Christ, and hidden messages all over the place. In fact, Genesis chapter one is one of my favorite chapters in the Bible. So one day, I asked the Lord to show me something that related to Him and I discovered the life of Christ or the gospel in the 7 days of Genesis. If your interested, you can check that out here....
http://www.theologyonline.com/forums...ad.php?t=90762
Also, all of the different types of offerings in the Old Testament are a foreshadowing of the sacrifice of our Lord, too. The grain offerings are symbolic of his body (bread) and the drink offerings are symbolic of his blood (wine) and the animal sacrifices, which consist of meat and blood is symbolic of both Christ's body and blood.
Oh, and to check out some interesting typifications of Christ in the Old Testament, please see this thread here...
http://www.theologyonline.com/forums...ad.php?t=90860
Anyways, besides finding Christ within the Old Testament, what other purpose does the Old Covenant serve? Well, the Old Covenant confirms New Covenant doctrines and helps gives us a glimpse where believers are headed in the future with their life in Christ.
What kind of New Covenant doctrines or teachings can we find in the Old Covenant? Well, I believe that God's plan of salvation has not changed. Believers thru out all points in time are justified by faith in the Messiah. The Old Covenant saint was circumcised in heart and the New Covenant saint is born again spiritually. Circumcision was an outward sign of a believer's changed heart in the Old, just as baptism is an outward sign or public declaration of a believer's new heart in the New. For Jesus was surprised that Nicodemus did not know about being born again. For all believers thru out all of time are reborn spiritually and justified by faith in the Messiah; And all believers thru out time had abided in the Son. For he that has the Son has life, and he that does not have the Son does not have life (
1 John 5:12).