Was Adam supposed to sin in God's great plan?
It has been argued that Adam and Eve did not sin when they partook of the forbidden fruit but that they only transgressed. Adam and Eve did not have a knowledge of good and evil until after they had partaken of the forbidden fruit. They definitely knew there would be consequences for their transgression but they didn't understand good and evil and did not really even know what death was at the time because they were in a state of innocence and had never seen or heard of death before. They also had never experienced deception and when Eve was told by the devil that she would not die, what reason did she have to disbelieve him. Adam and Eve were not like you and I who grow up in a world of deception and good and evil, they had no experience of such and only trusted in what they were told. Sin implies a knowledge that something is wrong or evil and yet is still indulged in. Since they were innocent not knowing good or evil, their transgression was not sin but only a transgression of the commandment. However, they did have free will and they chose not to obey the commandment and the prescribed punishment was mete out.
In Answer to this threads question, God did set up the conditions that Adam and Eve were placed in in the Garden and knew in advance that the fall would occur and did not avoid it. It was God's plan that his children go through a mortal probation. Here are the evidences for this:
1. God the Father foreordained Jesus Christ to be the Savior of the World before the foundation of this World.
1 Peter 1:19-21
19 But with the precious blood of Christ, as of a lamb without blemish and without spot:
20 Who verily was foreordained before the foundation of the world, but was manifest in these last times for you,
21 Who by him do believe in God, that raised him up from the dead, and gave him glory; that your faith and hope might be in God.
This occurred before Adam and Eve were ever placed in the Garden of Eden. This shows the omniscience of God and that he knew Adam and Eve would fall and thus prepared a way for Original Transgression to be forgiven and that if mankind would repent of their sins they could also find forgiveness of sin. The Atonement of Jesus Christ also provided for the resurrection of the dead so that when this life is over, all mankind will rise in the resurrection and become immortal and never die again. So this life simply becomes a time for mankind to gain a greater knowledge by experiencing good and evil, hardship, death, joy, love, hunger, fatigue, sorrow, etc., etc. In the end we will live in much better conditions and will never die.
2. In order for their to be evil in the world, God needed someone to influence mankind to disobey his commandments to do good. For this reason, after Lucifer rebelled against God in the War in Heaven, God cast Lucifer, later named Satan and Perdition, into this world along with his followers. Satan tempted the innocent Eve to disobey God's commandment regarding the tree of knowledge of good and evil. He and his followers also spend their time tempting all the rest of us to do evil as well. By learning to choose good over evil, we become stronger beings and become more like God. Throughout the ages, God has laid down his law letting us know what is good and by doing the opposite of good is evil. Thus by having a knowledge of good and evil, we then go beyond transgression through our disobedience to sin. God having foreknowledge of Adam and Eve's fall, He certainly could have kept the devil from being on this earth to tempt us. But he didn't. He placed him here so that we would provide opposition to his plan and thus we would have the need to grown strong in resisting temptation and becoming more like God himself in learning to choose good over evil. Those who not only learn to keep God's commandments but also learn to resist temptation and become much better and stronger people. Thus it was essential that mankind have a way to overcome their weaknesses through repentance and forgiveness of sin.
3. Just the sheer fact that God placed two innocent beings who had no knowledge of good and evil, deception, lying, or a remembrance of the the fall of Lucifer in a situation where this highly deceptive being would tempt them in their innocent state is more evidence that God knew that Adam and Eve would fall. It was as if God himself brought the entire plan into action. I believe he did just that because this earthly mortal probation is a necessary step in the progression of mankind to become being that are more like God. Free will is an essential part of mankind's progression. Without it there would be no progression. If there were no free will in this life, God would force us all to be good beings. However, that is not how beings progress to become good beings. You have learn to be good in and of yourself. You would not be a good being if God had to force you to do good for all eternity. To become good beings of one's own volition is the true path of progression. With free will, there will be those who do not choose good over evil but just the opposite. That is their choice. This life becomes a testing ground to see who will excel in doing good over evil. With free will some will choose to follow evil over good. That is a necessary drawback to the plan of progression. Free will ensures all will get what they themselves choose to receive. But God does not allow those who cannot obey his commandment into his kingdom. They will have to go to another kingdom if they are not willing to live the law of his kingdom. We are born with a predisposition to do good through that light of Christ that is given to every man and woman that enters into this world. It is through rejecting that light and choosing wickedness over goodness that we can loose that precious light that we are given in the beginning of our lives. By choosing good over evil, we receive more and more of the light in our lives and qualify for entrance into God's Holy Kingdom.