How do we know that apostasy is a serious issue?

Apostasy is addressed in the New Testament, especially in Jude and Matthew 24, where we see a clear warning against false teachers and a falling away from the truth of God's Word. Jude mentions that certain men have crept in unnoticed, ordained to condemnation, indicating that the church must remain vigilant. The warnings about false prophets and the prediction of a great falling away highlight the seriousness of this issue. Paul also alludes to these last days where many will depart from the faith, reinforcing the need for believers to be anchored in biblical doctrine and not be led astray by errant teachings.