The sin, both of men and of angels, was rendered possible by the fact that God gave them free will: this surrendering a portion of His omnipotence (it is again a deathlike or descending movement) because He saw that from a world of free creatures, even though they fell, He could work out (and this is the re-ascent) a deeper happiness and a fuller splendour than any world of automata would admit.
“Free will” is an unfortunate term for personal volition, implying that it is without cost. In its highest form it is Divine Sovereignty, but our loving Creator delegated some of that priceless divine attribute to us, fully knowing what our failure to correctly handle that gift would cost him.
That’s why I say the gospel of Christ didn’t begin with the eternal Word’s incarnation in Jesus of Nazareth. In fact, the entire history of God’s forbearance with troublesome mankind is his gospel (good news). God intended for his Law, delivered through Moses, to show his stiff-necked people the absolute impossibility of earning their justification in God’s eyes. Apostle Paul dealt well with that issue:
Galatians 3:1 O foolish Galatians! Who has bewitched you? It was before your eyes that Jesus Christ was publicly portrayed as crucified. 2 Let me ask you only this: Did you receive the Spirit by works of the law or by hearing with faith? 3 Are you so foolish? Having begun by the Spirit, are you now being perfected by[lit. now ending with] the flesh? 4 Did you suffer so many things in vain—if indeed it was in vain? 5 Does he who supplies the Spirit to you and works miracles among you do so by works of the law, or by hearing with faith— 6 just as Abraham “believed God, and it was counted to him as righteousness”?
23 Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. 24 So then, the law was ourguardian until Christ came, in order that we might be justified by faith
Romans 3:19 Now we know that whatever the law says it speaks to those who are under the law, so that every mouth may be stopped, and the whole world may be held accountable to God. 20 For by works of the law no human being will be justified in his sight, since through the law comes knowledge of sin. 21 But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— 22 the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: 23 for all have sinned and fall short of the glory of God, 24 and are justified by his grace as a gift, through the redemption that is in Christ Jesus, 25 whom God put forward as a propitiation by his blood, to be received by faith. This was to show God’s righteousness, because in his divine forbearance he had passed over former sins. 26 It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus.
Some may argue that some animals also possess free will, and anyone with a cat or dog would agree. Human volition is, however, at an exponentially higher level than that. Animals can’t anticipate their actions’ full range of moral ramifications. The viral, “Guilty Dog” videos show their reaction to chastisement, but that’s after the fact. I’ll close with one of those videos.