The relationship between Old Testament and New Testament?

The Old Testament has much value as it is the word of God and particularly, for Christian believers as it shows that the Law through its ceremonial and religious practices could not bring perfection. Particularly through the many prophecies about the coming messiah, which were clearly fulfilled precisely in Jesus Christ of Nazareth is it valuable, as well as the many things that are written in it 'for our instruction upon whom the end of the ages has come.'

Many New Testament doctrines are set out in the Old Testament and have abiding relevance such as the character of God as Creator (and many other attributes), the origin of sin (hence the need of a savior), the origin of marriage and of language and government. Many of these 'foundational truths' continue, especially as they are explained further under the Christian dispensation.

Religious practice in the Old Testament was more a matter of external observance of outward ceremonies by a priestly class, whereas the New Covenant or Testament which was specifically a matter of the heart, and clearly spoken of in the Old Testament as being more generally applicable to all.