הוי שקוד ללמוד תורה ודע מה שתשיב לאפיקורס ודע לפני מי אתה עמל (אבות ב:טו)
Rebbi Elazar says, be diligent in the study of Torah, and know what to answer to a heretic, and know before Whom you toil.
When asked by Rabban Yochanan ben Zakkai which is the proper way to which a man should cling, Rebbi Elazar answered, "a good heart." The Meforshim explain that the three instructions mentioned in the Mishna are three ways of acquiring a good heart. It is understandable how diligence in Torah study and knowledge before Whom one toils can be means of acquiring a good heart. However, it isn't clear how the knowledge of what to answer to a heretic can help one achieve this goal.
Rav Wolbe (Alei Shur vol. II p. 288) notes that Rabbi Elazar does not instruct us to answer heretics, since one should not enter into a dispute with a heretic. Rather, he tells us that one should "know what to answer" to a heretic. A person must have ironclad, crystal clear emunah to the degree that no one would succeed in budging him from his belief. In addition to the emunah rooted in feelings, it is necessary for emunah to be well founded in a person's intellect. Conviction in emunah (the knowledge that Hashem is the source of everything) is another means for acquiring a good heart.
There is no need for philosophical arguments or intense research. Every mentally sound individual should be able to arrive at the knowledge that Hashem created the world, gave us the Torah on Har Sinai and will eventually bring the redemption. It is clear beyond a shadow of a doubt that there is no way that our remarkable world could have possibly created itself. It also follows, that if there is a Creator of the world, He certainly informed His creations of the purpose of the world and gave them detailed instructions how to navigate life. Additionally, the revelation at Sinai was witnessed by millions of people and recorded in the Torah, and there is no documentation of any ancient writer who disputed this reality. We also can be certain of the veracity of what transpired since it has been passed down through our unbroken chain of mesorah of leaders who we know would never lie; beginning with Moshe and continuing with the Prophets, Tannaim, Amoraim, Geonim, Rishonim and Achronim.
Likewise, the need for a Final Redemption is rational. It is understandable that the Creator is not going to allow His creations to grope in the dark forever. The world was created with a purpose and when He decides that the goal has been reached, the world will cease to exist in its present state.
These are simple straightforward ideas that help a person strengthen his emunah; and there are countless other ideas and proofs that can do the same. Nevertheless, if a person doesn't give this topic any thought, he will be left with a half baked emunah that won't stand up in a time of need.
A person never knows where he might end up and he has to be spiritually ready for any situation. Yosef HaTzaddik was uprooted from his spiritual enclave and deposited in a depraved society where he spent more than twenty years without any spiritual backing. In Russia Jews were uprooted and placed in Siberia, and during the holocaust Jews were displaced from their communities. Rav Wolbe himself spent eight years alone in a country devoid of religious life. Hopefully none of us will ever have to endure such an upheaval, but nevertheless, our emunah should be able to weather any storm.
A practical suggestion to help implement this idea: Take some time to go through the Kuzari, Derech Hashem (Rav Wolbe in Alei Shur ibid. suggests both of them) or any of Rav Avidgor Miller's seforim. They have the ability to do wonders for your emunah.