We come to this world to learn. On the spiritual plane, which is our true home and point of origin, we exist in a state of peaceful bliss but without challenge. We are still united with our source though we are not able to comprehend that or express it in any serious or creative sense. If we are to engage with God in a more than passive way and if we are to be able to wield divine powers and energies ourselves as fully conscious beings then we must descend to the material world of choice, the only place in which we can begin to unfold our potential. In a world of oneness there is nothing to bring out innate qualities which will remain inchoate. Only when the reality of God is withdrawn from our awareness can we start to develop spiritually as real individuals. Intelligence needs problems in order to grow. There are none in the spiritual world. Also, the quality of the soul, meaning whether in a situation where God is not it will aspire towards him in love, cannot be determined unless the soul is given the choice to believe or not believe which it is in a material world where God is not obvious and you can (apparently) do without him. Here in this dimension of being the environment is such that God is not evident to the human mind. If it is open to God it can begin to be aware of him and the effort to become aware will increase the awareness. If the mind closes itself to God then the reality of God will become more obscure. To him that has more will be given, to him that has not even that which he has will be taken away. This might sound unfair until you realise that it is a simple fact of receptivity. The more the mind opens to God the more it can receive from him. The more it shuts him out the more it enshrouds itself in darkness.
It is not that we cannot learn and grow at all in the spiritual world. But there are certain lessons we can only learn here and certain tests we can only be subjected to in a world in which we have to choose between God and not God. In this world it is not just a question of choosing between good and evil. That's a fairly elementary decision to make but there is also the matter of spiritual good which is God and good as conceived in materialistic terms which may actually be spiritual evil if it denies God. Worldly people think of spirituality in ethical terms which could be summed up by the Golden Rule. But actually how people interact with each other on the material plane of being is a secondary consideration. That doesn't mean it is unimportant but the primary spiritual concern and the true test of the human heart is how you interact with God. Whether you acknowledge him or not and, if you do, how deep that acknowledgment goes.
That is the major lesson on this planet. To become consciously aware of God and then conform your soul to his. The best and easiest way to do this is through Jesus Christ but there is a catch. You can follow Jesus in your head or in your heart or both. The last two approaches to him work, the first doesn't.