It is good if we are able to see the Old and New Testaments as one book given to the church by God. If we do not already grasp this, then we must seek to rectify it. The fundamental thing is that God does not change. There are differences in the clarity of revelation: the New Testament is clearer than the Old, but both have one message, and that is the great provision that God has made for the salvation of His people. This provision is promised in the Old Testament, and actually provided in the New. The best link between the Old Testament and the New is the book of Hebrews. A key phrase is found in Hebrews 10:1, which tells us that the law has a “shadow of good things to come, and not the very image of the things”. We must keep that word ‘shadow’ before us continually as we read the Old Testament, because there are in it many shadows, or foreshadowings of the Gospel, and especially of Christ. We sometimes call these shadows, ‘types’, but it is simpler for us, to begin with anyway, to think in terms of shadows, or foreshadowings.
In Isaiah 55 verse 3, we have the wonderful gospel invitation: “Incline your ear, and come unto me: hear, and your soul shall live: and I will make an everlasting covenant with you, even the sure mercies of David”. The word “covenant” appears in the bible over 230 times, and yet the word and concept of ‘covenant’ has almost disappeared from the vocabulary and preaching of the church. This is a great loss. We hear much about God’s promises, but little about ‘covenant’. Some think that promise and covenant are the same thing. They certainly are related, but ‘covenant’ takes assurance of salvation much further than promise. In Hebrews 6:17 we read of God’s desire to show His beloved people, the unchangableness of His purpose, which he confirmed to them by an oath. When God makes a covenant He is taking an oath: He is swearing by Himself because He cannot swear by any greater. We shall, in a moment, look more closely at the procedure involved in the making of a covenant, but first of all let us continue to consider God’s reason for giving His people more than a promise of the security of their salvation.
In Hebrews 6:18 we have the reason for covenant as well as promise: “That by two immutable things in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us”. This shows us God’s loving concern that His people would feel doubly secure in their salvation. It is not that God’s promise was not in itself secure, but that God in His love, and His understanding of human weakness, goes, as it were, the second mile to assure them that their salvation is secure.
So when did this covenant oath come into being? In Genesis 15, we have one of the most awesome passages in the whole of scripture. Covenants were common in the ancient world. When two people entered into a contract where absolute trust was required, the ritual was that they slew some animals, cut them into pieces, and divided the pieces into two heaps. Each of the participants then stood at opposite ends of the space between the two heaps, and at the climactic moment, they each walked in opposite directions through the space. They were each taking an oath that if either broke the covenant, they would be divided as the animals were, in other words, they would be killed. Now the amazing thing about what happened in Genesis 15 is that only God, made visible as a “smoking furnace and a burning lamp”, passed between the pieces, and Abraham did not. God was saying, ‘If I break My covenant, I will cease to exist! I stake not just My honour, but My very existence on the keeping of this covenant’. How secure is the child of God? He is as secure as the very being of God Himself.
So to return to the wonderful invitation of Isaiah 55:3, the promise to all who come to God to receive His great salvation is “I will make an everlasting covenant with you”. God is saying to every sinner that comes to him, ‘I bind myself to you in an eternal bond and I will stake my honour on securing your salvation’. God makes exactly the same promise to all who, in New Testament times, receive God’s provision for their salvation in Jesus Christ. God does not change. All who were saved in Old Testament times were saved through faith in the coming Saviour. There is, never was, and never will be, any other way for a sinner to get RightWithGod.