Do angels have a sin nature?
No. Angels, unlike flesh and
blood men and women, know Almighty
God in all His fullness, that is,
His power and glory. They were
created perfect with perfect
knowledge. They were also created
with personal volition or "free
will." They can make choices. One
third of the angelic forces chose to
follow Lucifer in rebellion against
God.
Because they know God --that He
is the only God-- the angels can't
be redeemed once they reject God's
rule over them. They already have
perfect knowledge of the Creator of
all things.
Man was not given the knowledge
of good and evil in the beginning.
Rather, he having been also created
with free will chose wrongly based
at least in part upon his lack of
full understanding. Man, therefore
has a means of Redemption available
to him through Christ's shed blood,
because he (man) must come to the
knowledge that he needs the Savior,
Jesus Christ.
Mankind needs salvation because
Adam and Eve disobeyed God and fell
out of fellowship with Him when they
disobeyed Him and ate fruit from the
tree of the knowledge of good and
evil. From that point on his nature
became sinful.