In Genesis 2:17, is God telling a lie for a greater good?

Briefly, in the Bible the word death has a couple of meanings. One is often described as spiritual death. This is similar to death meaning, "dead to the things of God". The natural man, not a Christian, is unable to perceive the things of God, much like the Pharisees and Saducees in the gospel were unable to perceive that Christ is the Son of God, the Father, and ultimately God Himself. A more direct answer to the question and in agreement with the previous two variations, death is separation from God. Even those who spend in eternity in hell, are alive in a sense. However they are separated from God. In another sense, this separation is an eternal death. So in all three meanings they died that day, being separated from God, like us they became unable to perceive God and dead to the things of God. All three of these fully applied when God evicted them from the garden.

The Bible uses death to describe the spiritual state of people who are undoubtedly physically alive. Notice Romans 5:12: “Therefore, just as through one man sin entered the world, and death through sin, and thus death spread to all men, because all sinned.”
from What Does the Bible Say About Death as Separation from God?

Many passages such as Romans mention this in various words.

Note: in the New Testament, the book of Romans and other passages write those who have been baptized into Christ are baptized into his death and raised unto newness in Christ. The sinful nature, including inability to perceive God no longer rule our lives. Under the New Testament, Christians may perceive the mysteries of God as Paul did and are no longer dead to the things of God.

1. I don’t know for sure that this Hebrew word תָּמֽוּת׃ means to die immediately and physically. In Gen 35:18, Rachel dies and “she called his name Benoni”, afterward. But then she was buried. I believe elsewhere it meant dead to God, to the Spirit. My understanding of the story is that their spirits immediately left. Instant spiritual death. “Spirit will not occupy a dirty house” is how I heard one preacher out it.

2. More importantly, it is very difficult or impossible to know what in the Bible is metaphor and what is literal/historic. We certainly cannot say that nothing is metaphor. Even the disciples said plainly that Christ spoke in metaphors. I don’t think it’s reasonable to assume that every single metaphor is clearly delineated as a metaphor:

Through time, it becomes more clear that the Bible, especially KJV, is a collection of the words of God inspired through and for the human race over thousands of years, revealed and tabulated and collated and protected for the English speaking man. And that Jesus Christ the Lord is real and saves those who accept and proclaim Him as Lord, the Lord and Savior Who came in the flesh to die and be resurrected for us. God has made a plan and a pact and communicated it to us.

I do not know the details beyond this reality and I don’t especially dispute those who claim to know; they might, but it has never been given to my heart and soul (or even my intellect by honest and sincere study) that every incident is a historical fact. That may one day change. If someone convinced me that it was indeed meant to be taken literally and factually I would. This story may be the wisdom of the ages outlined in metaphor, in a way we can understand, how we ended up in this predicament of sin, and later how He gets us out of it. Seeking the real Christ and the living waters through reading and praying and fasting and putting God first is more important. Accepting the Truth, the loving Christ as savior as Lord and repenting is most important.

Good question. Per the notes from the Net Bible below, there are several possible explanations. I would add that what we have in Genesis is surely only a summary of God's interactions with Adam and Eve and it is reasonable to assume God may have made Himself clear in other ways as well. Moreover, even if Adam and Eve did not fully understand what God meant, that is not the same as God lying. Think of when we warn a child of danger like burning their hand on the stove, the child cannot understand fully if they have never been burned - they must trust their parent's judgment.

• given that they were immortal as long as they ate of the tree of life, the meaning here could be that they would become mortal if they disobeyed God. This could be true even if the literal meaning of the words was that they would die immediately - not all language is literal. For example, in English, "Mom is going to kill you" can simply mean "You're in big trouble". Hebrew is an ancient language so we must be careful when drawing these types of conclusions from the English text.

• God had mercy and extended their lives

Net Bible Notes - https://netbible.org/bible/Genesis+2

Or “in the very day, as soon as.” If one understands the expression to have this more precise meaning, then the following narrative presents a problem, for the man does not die physically as soon as he eats from the tree. In this case one may argue that spiritual death is in view. If physical death is in view here, there are two options to explain the following narrative: (1) The following phrase “You will surely die” concerns mortality which ultimately results in death (a natural paraphrase would be, “You will become mortal”), or (2) God mercifully gave man a reprieve, allowing him to live longer than he deserved.

Heb “dying you will die.” The imperfect verb form here has the nuance of the specific future because it is introduced with the temporal clause, “when you eat…you will die.” That certainty is underscored with the infinitive absolute, “you will surely die.” sn The Hebrew text (“dying you will die”) does not refer to two aspects of death (“dying spiritually, you will then die physically”). The construction simply emphasizes the certainty of death, however it is defined. Death is essentially separation. To die physically means separation from the land of the living, but not extinction. To die spiritually means to be separated from God. Both occur with sin, although the physical alienation is more gradual than instant, and the spiritual is immediate, although the effects of it continue the separation.

God told no lie. He told the couple absolute truth when he warned that if they partook of something that appeared to be good and desirable (the forbidden fruit), they would die. And die they did. In a two-fold sense they died.

Given that they had not partaken of the fruit of the Tree of Life, they were not immortal. That is why God debarred them from access to it after both physical and spiritual death began to take effect on them. The Tree of Life only reappears in the Book of the Revelation, in the new heavens after all sin has been dealt with. Until then, all humanity suffers the corruption of the flesh that starts after birth and ends in physical death. "Life is a terminal condition" goes one saying. And all humanity born physically starts in a spiritually dead condition. To live without death is what happens to humans who believe what God says on the matter of life. Jesus confirmed that in his gospel, so that all who believe and trust Jesus pass over from death to life eternal. That is why he said that all who believe in him will never die (even though they may die physically.) Yet, until they do that, they are spiritually dead. They have to be born again, of the Spirit, to come to spiritual newness of life.

Spiritual death happened to Adam and Eve after they disobeyed God, within that very day. And within a symbolic 'day' in God's timing (1,000 earth-years) they had grown old and died physically. But that day in the Garden of Eden, they immediately knew they'd spoiled their relationship with God, seeking to hide from God, and to cover themselves (literally, with fig leaves, and symbolically by blaming others. Adam ultimately blamed God! "The woman thou gavest me..."!)

God knew what they had done but asked them to admit it. God had alerted them to a grave danger [pun intended]. The opposite of life - death - would happen if they partook of one particular thing. "Don't do that. Don't go there. Don't think you can live as I do by choosing a different way than the one I give" (not a verbatim statement, but that's what was involved).

God does not die. He is the source of all life, the great "I Am", who is utterly holy, righteous and almighty, and who gifts life eternal in Paradise to those he chooses. He does not gift life eternal to those who wilfully disobey him, for that is the path of unholiness, unrighteousness, and mortality. Now it is time to consider God's warning about death, as epitomized by eating one forbidden 'fruit'.

There was an enemy of God out to wrest God's sovereign and legal rule over his creation through deception - an illegal take-over-bid was made in Paradise, and the unseen deceiver utilized a creature in the garden to introduce an idea that would lead to death, but (obviously) without hinting at that. Quite the opposite. The deceiver first questioned what God had actually said, then ever so slightly twisted what God had said, then implied that if the humans disobeyed God they would not die but they would steal a march on God and become like him. The idea was that God was holding something back from the couple, and his warning of death was just not true - the opposite would happen. Without eating of the Tree of Life, they could grasp that divine life by knowing what this other 'fruit' was. But they had to partake of this other 'fruit', to find out. Then their eyes would be opened and they would be raised above their already glorious status as made in the image of God.

If the couple had had faith in God their Creator, who had gifted them life on a glorious planet, with every need and good desire already met, they would have been allowed to partake of the Tree of Life. But they failed to trust God, who does not lie. Who cannot lie, otherwise he would not be God!

So, the simple answer to your question is that God told no lies, but the great deceiver lied, for the greater evil. And he's still at it, trying to twist what God has actually said to make people think God is lying. Don't fall for it.