From According to Plan by Graeme Goldsworthy (p 50) :

Every word of the New Testament comes from the Holy Spirit’s testimony to Jesus. The New Testament records the central facts of the gospel and explores the implications of the gospel for the lives of God’s people. It shows us that the gospel is God’s one way of bringing sinners to perfection. All the problems and imperfections that we experience are failures to be conformed to the gospel. The only remedy that the New Testament prescribes for our problems is to bring our lives to conform to the gospel.

Likewise, the one problem we have in the interpretation of the Bible is the failure to interpret the texts by the definitive event of the gospel. This has its outworking in both directions. What went before Christ in the Old Testament, as well as what comes after him, finds its meaning in him. So the Old Testament must be understood in its relationship to the gospel event. What that relationship is can only be determined from the witness of the New Testament itself.