God isn't mumbling crazy impossibilities, heresy, or idle threats into the air to keep us secure. His warnings are true and their consequences are real, for His word is truth (John 17:17). One need only look at the admonitions in scripture to see what the apostles taught concerning security in Christ.
Between we have all manor of views, so I will just share my own. Perseverance is necessary for salvation. God preserves His people through middle knowledge, such that we can, but will not fall away. God, knowing how we will choose in various circumstances, puts us only in those circumstances that keep us in the faith. Breaking the Law of Moses could never causes us to loose our salvation, but unbelief could. But God keeps us from unbelief.