"For this world is the opposite of heaven, being made to be its opposite, and everything here takes a direction exactly opposite what is true. In heaven, where the meaning of love is known, love is the same as union. Here, where the illusion of love is accepted in love's place, love is perceived as separation and exclusion." ACIM Txt. pg. 341
This world is the opposite of heaven. Everything separate - identities (via the ego), physical forms, opinions, beliefs, skin colors, separation of a baby from its mother at birth, separation of a body from the world and its family at death - all of it is opposite of heaven, because in heaven, all is love, all is union and wholeness, which is the make-up of God.
We live in this world and we react to the multitude of difficulties we think we face here, but in reality, anything of this world is an illusion, one we made up to "hide" from God, to be gods to ourselves. We have buried God and the love and peace and joy we could experience by uniting our minds with His, under a blanket of ego that keeps His face hidden from our view, Yet, by looking on the face of Christ (and using Jesus' face in form if a symbol is needed?), we can come to remember who we truly are and when we remember, we can go home. The way to remember is through forgiveness of everything in this world and forgive our brothers because our brother's actions or inactions or whatever grievances we hold against him, are untrue and never occurred at all.