From What Do Sins Originate?

QUESTION: From what cause does the act of sin in man originate?

ANSWER: The free will is the first cause of its own moral acts, just as God is the first cause of all created being. A first cause is unthinkable; we cannot mentally construe either the absolute, like a first cause, or the infinite, like a succession of causes running back without end. Man is the creator of his own character and destiny. The most important part of God's universe is left for free agents to create — moral character. When it is completed at the close of each one's probation, whether the character is good or bad, God. cannot arbitrarily interpose to change it. As the free agent has fixed it so it must remain eternally.

— Steele's Answers pp. 212.