One of the great treatises on the person and work of Christ is the work entitled On the Incarnation of the Word by Athanasius. The entire treatise is worth a careful read as the author takes the reader carefully through a journey of understanding why the person of Christ, as fully God and fully man, was so necessary in accomplishing the work of atonement. Here is how he describes the death of Jesus on our behalf.
The body of the Word, then, being a real human body, in spite of its having been uniquely formed from a virgin, was of itself mortal and, like other bodies, liable to death. But the indwelling of the Word loosed it from this natural liability, so that corruption could not touch it. Thus it happened that two opposite marvels took place at once: the death of all was consummated in the Lord’s body; yet, because the Word was in it, death and corruption were in the same act utterly abolished. Death there had to be, and death for all, so that the due of all might be paid. Wherefore, the Word, as I said, being Himself incapable of death, assumed a mortal body, that He might offer it as His own in place of all, and suffering for the sake of all through His union with it, might bring to nought Him that had the power of death, that is, the devil, and might deliver them who all their lifetime were enslaved by the fear of death.
Mankind was brought from corruption to incorruption through the cross, wherein Jesus defeated sin, death, and Satan.
The chief meaning of the cross is that there ‘the powers of death have done their worst’ and have been defeated. So the cross is above all the trophy of victory, that victory which is first Christ’s and then also ours as we live in him.
Athanasius ties this idea of Jesus’ death closely to his resurrection, demonstrating that we now receive salvation and await our own resurrection because of Christ’s work on our behalf. This is a beautiful and glorious picture, demonstrating why it is worth our time and effort to know the person and work of Christ in a thoroughgoing and intimate fashion.