Humans seem to widely intuit that it is a great good for us to make self-forming choices. For example, our showing courage and thereby becoming naturally courageous is an intrinsically good thing.1 This extends to desirable spiritual states in general that we might not otherwise attain.
Richard Swinburne (Philosophy professor at Oxford): “Yet it would seem a good thing that a creator should allow humanly free creatures to influence by their own choices the sort of creatures they are to be, the kind of character they are to have. That means that the creator must create them immature, and allow them gradually to make decisions which affect the sort of beings they will be.” [“The Problem of Evil” Online at mind.ucsd.edu]
• John Hick: “[Virtues] which have been formed within the agent as a hard won deposit of her own decisions in situations of challenge and temptation, are intrinsically more valuable than virtues created within her ready made and without any effort on her own part.” ["An Irenaean Theodicy," reprinted in Mesle, John Hick's Theodicy, xxii.]
• John Hick: “[One] who has attained to goodness by meeting and eventually mastering temptations, and thus by rightly making responsible choices in concrete situations, is good in a richer and more valuable sense than would be one created ab initio in a state either of innocence or virtue . . . [It] is an ethically reasonable judgment, even though in the nature of the case not one that is capable of demonstrative proof, that human goodness slowly built up through histories of moral effort has a value in the eyes of the Creator which justifies even the long travail of the soul-making process.” [Evil and the God of Love (Harper and Row, 1977), 255-56.] Similarly, Joseph Butler: “[It is appropriate that we] should be placed in a state of discipline and improvement, where [our] patience and submission is to be tried by afflictions, where temptations are to be resisted, and difficulties gone through in the discharge of our duty.” [Fifteen Sermons, 235.]
It is good for agents to be able to make free self-forming choices, orienting themselves to the good (and God) for eternity. This is relevant because it might be that only upon forming our characters in such a way on Earth (with God's aid and where temptations for evil are strong) that we would be suited to naturally and freely choose the only good forever more in Heaven. After all, it may be possible to sin in heaven, but far less tempting. (That is to say, it may be that living a perfect life requires virtually no effort at all for those who in part forged themselves for good on Earth).1
But wait, isn't it impossible to form one's own character? [See response]2