The Road to Apostasy

Apostasy - also known as falling away, abandoning the faith, or the
recent woke term "Deconstructionism". What does the Bible teach
about this seemingly growing trend? What did the Church believe
about it until the 5th century? How/why did that change? What are
some of the factors that lead people to abandon the faith? How do
we know that we are currently "in the family"? What are the things
we can do to ensure we don't fall away?