God made man to be with Him for eternity. Yet, God made man knowing he would sin and be separated from Him. Why would He do this?
God made Adam and Eve to know and love Him and to share in his Divinity. Without the Law to abstain from eating fruit from the tree of knowledge of good and evil, Adam’s and Eve’s love would have remained in the sensuality (like a small child), a purely instinctive love and not an actionable love.
Imagine a child who loves his parents because they feed, clothe, shelter and love him, but they never give him instructions on how to behave; they never tell him what to do or not to do. In other words, the child is never given rules and, thus, is never given the opportunity to choose between good and evil, between love and hate (includes apathy).
Free Will and Choosing Love
With the Law to abstain from the fruit of the tree, however, our first parents could choose to love or hate God through obedience or defiance. When they ate from the tree, they acted against love and truth, and this act was contrary to God who is Love and Truth. Knowing they would sin and knowing we would suffer the effects of their “Original Sin” (deprivation of grace, inclination to sin, and physical/spiritual death), why would God have created them in this manner?
All rational beings (God, angels, humans) have free will. Free will in created beings provides the ability to sin against God or to love by obeying Him. God promised Adam and Eve eternal life provided they obeyed Him. Therefore, Adam and Eve would have lived forever, physically and spiritually, if they would have obeyed God for eternity; though, the potential to disobey God would have remained (see ST I, q. 100).
Adam and Eve ultimately disobeyed God and physically died. Most likely they died in a state of forgiveness, however. In this state of forgiveness, they were with God spiritually and their souls would have been imprinted with Divine knowledge giving their souls dominion over the body.
Consequently, they will no longer succumb to temptation and die. Their souls are fixed toward God and they will never experience death again. The second state is far better than the first state in which they and their progeny would have been continually tempted and could have died.
Putting this all together, we can see that God made man with reason and free will to give him the ability to love. God gave man a Law, so that man could put love into action. He did this knowing perfectly that man would choose to sin and die and, even if man had never sinned, the potential to sin would have always been present. He allowed this knowing that man would ultimately rise without the possibility of future corruption. For a human being, this scenario is the best way for him to choose God, who is Love and Truth, and live forever without the possibility of sinning or of future death.