Although the Catholic church views the fall of man in the Garden of Eden as a terrible mistake, the Orthodox church sees it as a necessary step in the ladder of progression. When Jesus was resurrected, he became a being of immense power and glory with a perfect body of both flesh and bone (no blood, which is the corruptable part of man). "For a spirit hath not flesh and bone as ye see I have."
All men, because of the redemptive power of the atonement, are likewise resurrected in the flesh, from the greatest to the least, but Paul tells us that that not all will be raised to the same glory, for as heavenly bodies differ from earthly bodies, and as the sun, moon and stars differ from one another in glory, "so also is the resurrection." (See I Cor. 15) When all are judged, all will resurrected according to that judgment.
But this is only possible because of the atonement.
If man had not transgressed in the Garden, he would have remained forever with no glory on the earth or throughout the eternities, forever miserable because he knew no good from evil. To understand happiness he had to know sadness; to know joy, he had to understand sorrow. It was all part of the plan of salvation, but the Lord wanted it to be man's decision. He forbade it, but in the next breath said, nevertheless, it's your decision.
John said, speaking of the elect, "For when we see him, we shall be like him, for we shall see him as he is." And since Jesus was resurrected as a perfect being of flesh and bones, man also has that potential.
Adam and Eve were both terrestrial in nature. Their bodies were not perfect because they contained no glory and no power. They were limited only to this world and if they wanted to go somewhere they had to walk. Knowing neither good nor evil, they lacked the ability to progress and grow. And though it never says, it's also unlikely that they could have reproduced. So they were set up to fall, and it had to be their decision.
They were put into their environ with a tree, the fruit of which could make their bodies corruptible. Also there was a fallen archangel to tempt them. They also were given time to themselves. In other words, all the elements were there for it to happen. All Adam and Eve had to do was pull the trigger. But the Lord's intentions were to make them like He, Himself, and this is why the fall had to happen.
