“Now the serpent was more crafty than any of the wild animals the Lord God had made” (Genesis 3:1).
The Bible doesn’t begin with the beginning of evil, but its existence. Humanity is created innocent, creation is good and the deceitful serpent is already there.
How did the serpent become deceitful and humans become susceptible to temptation? I don’t know. I believe that angels and humans were created with free will, but that doesn’t explain why good creatures with good hearts experience the imperfect impulse to rebel. Free will is an accurate description of the first created beings, but not a full explanation of why they sinned. Free will is a name for a mystery.
Here is what I can say: God is sovereign. Nothing happens apart from God’s plan. God causes some things directly and permits others indirectly. The serpent’s desire to deceive the first humans into rebelling against God, and humanity’s succumbing to temptation were all a part of God’s plan of salvation. Sovereignty is an accurate description of God, but not a full explanation of why the rebellion was a part of God’s plan. It’s the name of a mystery.
I end where I began: how the very first sin in the universe came about is a mystery to me. I do know that God demonstrates both sovereignty and holiness again and again in the Bible. God is sovereign over all things, including sin, and God is never a sinner.