Try to be at peace with everyone, and try to live a holy life, because no one will see the Lord without it.
This is a power packed verse, and I think we "Christians" do not grasp the depth of what is being said here...the admonition of how we are to live. God is often just a convenience to us to pull and use when we need Him...like a Kleenex. But when we are faced with instructions on how we are to live, we tend to think they are optional.
This scripture speaks to me the simple truth that if we hope to see the Lord, we must live a peaceful and holy life. We cannot do that on our own...we must have the Holy Spirit living within us to empower us to be peace loving and to live lives set apart for God's use.