Studying the real meaning of unbelief can indeed be helpful!  Scripture makes it clear that there is a great difference between unbelief and doubt.  Doubt is a season of unwelcome darkness, but unbelief is a refusal to believe.  The will is involved.  Where there is unbelief, truth is rejected by choice.

See John 3:36.  “Whoever believes in the Son has eternal life, but whoever rejects (does not obey) the Son will not see life, for God’s wrath remains on him.”

Scripture shows us that unbelief, disobedience, and disbelieving truth are synonyms.  Study Hebrews 3:7-19.