Peter said he would rather die with Jesus than deny Him. Then he denied Him. What about you? What about me? This passage of Scripture has many lessons for us in theology and apologetics, but what stands out to me the most is the lesson of how suffering and confusion test our faith in such a dramatic way.
Here is a link to the entire Mark series, going verse-by-verse through the Gospel of Mark looking for theological, historical, apologetic, and practical insights.