השב תשיבם לאחיך, "be sure to restore them to your brother.⁠" The Torah commands that we be very cautious to observe the commandment to restore lost property to its owners. Concerning the repetition of the words השב תשיבם, "be sure to restore,⁠" our sages in Baba Metzia 30 explain that one has to keep doing this even 100 times if necessary. All of this is part of the paths of mercy and kindness which we are to practice vis-a-vis each other seeing we are all the sons of one father. As such each one of us is vitally interested in what is useful for his fellow. We express our pity for lost property of our brother in practical terms by restoring it to him whenever possible. It matters not whether our brother has lost inert possessions or livestock such as his ox or donkey. Any kind of lost property is included in the Torah's directive to restore it to the loser. This wording refers to minor utensils worth less than a garment, livestock, etc., which we have found and which can be identified by the loser. The positive commandment is followed by the negative one not to try and escape this obligation by turning a blind eye and not picking up the lost object for oneself either.
There is more to the commandment to restore lost property than merely the act of restoring it. If a person is in a position to perform a useful service for his fellow and to thereby protect his fellow against financial loss, this is all part of the commandment under discussion here. All of this is part of the "umbrella" commandment in Leviticus 19,18: "love what is your fellow's as if it were your own!⁠"
Concerning the practical ramification of the words: "you must not hide yourself" (from your brother's lost property), and the subsequent semi phrase (verse 4) "you may hide your self from them,⁠" the sages in Sifri have this to say: if the finder is an aged individual, a scholar, and it is not in keeping with his dignity to carry a bulky object in order to fulfill the commandment (personally) to restore this object to its owner, the Torah permits such a person to turn a blind eye to the object he has found. Ordinary individuals, on the other hand, are not permitted to use this ruse.

A Midrashic approach. The words: "you will hide yourself from them,⁠" refers to what you may succeed in doing vis-a-vis your brother, vis-a-vis human beings; the words: "you must not hide yourself from them,⁠" refer to God who knows your motivation and whom you cannot fool by pretending not to have found the object or animal the return of which would cause you inconvenience or expense.

If you investigate this commandment still further you will derive from it encouragement regarding the subject of the resurrection. God will practice this commandment personally by restoring the souls of the departed bodies to their original owners in due course after the redemption and the arrival of the messiah. Each person will resume his or her original role in the universe. At that time "lost" property will truly be restored to its original owner. The most recent owner of that property will give it to the previous owner and so forth until it will be eventually restored to the very first owner [who had not deliberately abandoned it, Ed.]. This is what is alluded to in Psalms 139,16: "your eyes saw my unformed limbs.⁠" David describes that Adam's mental eye had been shown every human being ever to be to be born. [God had shown him the history of mankind in capsule form prior to his sin. This is why he donated 70 years of his life to enable David to be born alive at all as he had been shown a stillborn David. Since God had foreseen it, it was included in the book of the descendants of Adam he showed to Adam. The entire verse in Psalms 139,16 deals with this phenomenon. I refer the reader to an analysis by Rabbi Moshe Alshich in his commentary on Tehillim, this editor's translation page 1005. Ed.].
It is not clear whether at that time the original wife will be restored to her original husband [assuming she had remarried, or to her last husband on earth, or, whether God will add to such bodies by splitting the raw material much as we know that a light can be split].
All our sages are agreed that the commandment to restore lost property applies only to property belonging to Jews, not to that belonging to Gentiles. This is why the Torah stresses repeatedly אבדת אחיך, "lost property of your brother,⁠" and "restore it to your brother.⁠" Gentiles are perceived as part and parcel of אלו-הי נכר הארץ, part of the alien deities of "earth,⁠" a system of life which does not know of an hereafter or resurrection, etc. The Jewish people who are "God's share and inheritance,⁠" have a claim to eternal life and therefore it is mandatory that seeing their property is not lost permanently, that it be restored in due course. Regarding the resurrection of the dead, the Jewish people have been told (Isaiah 26,19) "Oh, let your dead revive, let corpses arise!⁠" whereas in verse 14 of that same chapter the prophet says "they are dead, they can never live; shades, they can never rise" (referring to the Gentiles).
Seeing that in connection with lost objects or animals the Torah employed the expression נדחים, "cast off, rejected,⁠" the Torah continues in verse 3 with the statement: "you must not hide yourself (if you found it). The moral lesson is: "do not hide yourself from the Lord, so that when the time comes He will not hide Himself from you,⁠" i.e. become someone whom you have "lost" (compare Samuel II 14,13-14).