Apologetics is the discipline that deals with a rational defense of Christian faith. It comes from the Greek word apologia which means to give a reason or defense. The most important reason to do apologetics is that God told us to do so.
The classic statement is 1 Peter 3:15, which says, “But in your hearts set apart Christ as Lord. Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect”(1 Peter 3:15).
This verse tells us to be ready. Being ready is not just a matter of having the right information available, it is also an attitude of readiness and eagerness to share the truth of what we believe. This is essential to both pre-evangelism as well as evangelism in the 21st Post-Modern culture we find ourselves in today. (Norman Geisler, Bakers Encyclopedia of Christian Apologetics, pg. 37)