Andy Stanley has recently and rightfully come under fire for his diminution of the Old Testament for 21st century evangelical Christians. He offers the church a sort of quasi-Marcionism that would elevate the New Testament Jesus while denigrating and antiquating the Old Testament God; as if the latter has no real meaningful relationship with the former. But anyone aware of Holy Scripture’s sense, meaning, and trajectory will almost immediately recognize how far Stanley has slipped into the absurd.
As Thomas Torrance has done, in his little book The Mediation of Christ, all Bible interpreters ought to recognize how central the Old Testament witness and reality is to the New Testament witness and reality. We ought to appreciate that the Old Testament and New Testament have the same canonical and regulative reality (res) in Jesus Christ; and read them together as a piece. This is where Stanley et al. fail to read the Bible accurately, and with any sense of theological acuity. He ironically stumbles just on the scandal of the Gospel as that has history of salvation sense – as that has protological gravitas in the promises of the Old Testament. He stumbles because he doesn’t read the Bible eschatologically; as if the circle of God’s Triune Life doesn’t sit above in the heavenlies breaking in and throughout the histories of the Old and New Testaments as a canonical whole. He stumbles by not seeing the face of Christ in the first Adam, the Israelites, the kings and prophets, and the suffering servant of Jobian and Isianic motif.
Along with Thomas Torrance et al., Karl Barth also understands the significance of the Old Testament; he gets how the New Testament would make absolutely no[n] sense without the context of the Old. Here Barth operates in a very catholic sense as he, along with many of the Patristics, counter someone like Marcion, and underscores the significance of the Old Testament reality for the New Testament Christian; as that all is conditioned by Jesus Christ.
To indicate the axiomatic character of the statement that Christ was manifested as the Expected One even in the time of the Old Testament, we may make the further point that this statement was one which was taken for granted by the whole of the early Church from the 2nd century up to and including the Reformation and the orthodoxy of the 17th century determined by the Reformation, in spite of all the changes in the interpretation and evaluation of the Old Testament. Marcion in the 2nd century and the Socinians in the 16th were already in the eyes of the Church of their time regarded as opponents of the Old Testament, theologians with whom one could not discuss, against whom one could only dispute as against heretics—in fact the last resort could not dispute at all, because in abandoning the Old Testament they had abandoned not something but everything, namely the New Testament itself as well, and the whole New Testament at that. No-one can annul or take away the Old Testament without also confounding the New Testament, since the new appeals again and again to the old as it stands in itself (Quenstedt, Theol. did. pol., 1685 I, c. 4, sect. 2, qu. 5, beb. obs. 5). So obvious to the early Church was the recognition that Christ is also manifest in the Old Testament. A. v. Harnack, who admittedly had no desire that this recognition should prevail, in his spirited way propounded the thesis that “to reject the Old Testament in the 2nd century was an error which the great Church rightly rejected; to cling to it in the 16th century was a destiny from which the Reformation could not yet withdraw; but still to preserve it after the 19th century as a canonical source in Protestantism is the result of a religious and ecclesiastical paralysis. … To make a clean sweep at this point and honour the truth in confession and instruction is the mighty act—already almost too late—required to-day of Protestantism” (Marcion, 2nd edn., 1924, 217, 222). Upon which the simple comment to be made is that by this “mighty act” the Evangelical Church would lose her identity with the Church of the first sixteen centuries, “The Gospels are ‘the flesh of Christ’ and the apostles the priesthood of the Church,” writes Ignatius of Antioch; “but leave us also the dear prophets, because their proclamation also aims at the Gospel, because they too hope for and expect Him, are saved by faith in Him, being in unity with Jesus Christ … witnessed by Jesus Christ and counted with Him (Ad Philad. 5, 2). They lived according to Jesus Christ, in spirit they were His disciples and were expecting Him as their Teacher; they were persecuted for His sake and were moved by His grace (Ad Magn. 8, 2; 9, 1).
It seems like it should be as simple as the way Barth puts it. It seems like the Christian should easily recognize how important the Old Testament not only was, but remains in the face (prosopon) of the risen Christ! But nothing is ever this simple in the confusion and morass that is the human complexity. Nevertheless, the clarion voice of the living Christ shines brightly through the halls of catholic and canonical history with all those with ears to hear, and eyes to see.
 Karl Barth, Church Dogmatics I/2 §14, 75-6. The italics are Latin and Greek sections offered in the English translation.