tl;dr: If hatred finds a place within your heart, you will perceive a fearful world.
“… learn and do not let your mind forget this law of seeing: You will look upon that which you feel within. If hatred finds a place within your heart, you will perceive a fearful world… If you feel the Love of God within you, you will look out on a world of mercy and of love.”
— A Course in Miracles, LESSON 189
This is a concise description of the way we shape our own, illusory version of reality, and how salvation is a joyful choice we make.
It is definitely not a prescription or dictate for the ego to do what it cannot do (i.e. to love). If it were, that would only make us feel guilty about our failure, and thereby reinforce the ego mindset of separation.
Fear, hatred and guilt are just thoughts. Everything we take for real is a thought of separation, and a judgment about truth. Without realizing it we are the prisoner and sickly victim of our own judgments, which are never true, although we firmly believe they are.
The body is a thought, the world is a thought, the ego is a thought. We are not our thoughts.
True reality cannot be thought, judged, or understood in any way, but we also cannot avoid simply being it.
Becoming aware of our illusory ego thoughts, and observing them without judgment, is the way to render even the most persistent illusion powerless.
Simply observing our mind is an act of love, and happiness is an attribute of love. What more could we want? Losing an illusion, something that doesn’t exist, is not a loss at all.
“Why wait for Heaven? Those who seek the light are merely covering their eyes. The light is in them now. Enlightenment is but a recognition, not a change at all. Light is not of the world, yet you who bear the light in you are alien here as well. The light came with you from your native home, and stayed with you because it is your own. It is the only thing you bring with you from Him Who is your Source. It shines in you because it lights your home, and leads you back to where it came from and you are at home.”
— A Course in Miracles, LESSON 188