“I will put enmity between you and the woman, and between your offspring and her offspring; He shall bruise your head, and you shall bruise His heel.” - Genesis 3:15
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The first promise of Christ was given in the very beginning, when man by sin had cast Himself into misery and ruin. Yet God, in His infinite grace, revealed that One should come who would repair all the breaches made by the fall. From that hour the expectation of the church was fixed upon Him who was to come. All the promises of God from that time were centered in Him alone. Not one blessing was to be obtained but by virtue of the mediation of the promised Redeemer. Hence the whole faith of the ancient church consisted in waiting for the coming of Christ.
There was nothing of God revealed or obtained but in and through Christ. All gracious manifestations of God, all communications of His love to His people, were through Christ alone. From the beginning, He was the foundation of all covenant-transactions. Though He was not yet come in the flesh, yet the virtue of His person and mediation extended itself unto all ages. The saints of old looked upon Him who was to come, and by faith derived supplies of grace from Him.
So all the prophecies, promises, and institutions of worship were designed to keep the hearts of believers steady in their expectation of Him who was to come. They were continual testimonies that God had not forgotten His word, nor would He fail in bringing forth the Deliverer in the fullness of time. The glory of Christ was the life and soul of all true religion from the beginning; and it is the desire of the church in all ages to behold that glory.
(Taken from The Glory of Christ by John Owen)