[Alcuin]

For my two bits on this – FWIW, that is –

I’m inclined to agree with a number of points:

• Hammond and Scull’s assertion,

  …its keeper never abandons it. At most he plays with the idea of handing it on to someone else’s care – and that only at an early stage, when it first begins to grip. But as far as I know Bilbo alone in history has ever gone beyond playing and really done it. – This is true of the One Ring, but not of all Rings of Power, of which Gandalf seems to be speaking generally. Celebrimbor gave away the Three Rings. Círdan gave his Ring to Gandalf, Gil-galad (when dying) gave his to Elrond, and Thrór gave his Ring to Thráin.

• “[T]he Three are not ultimately comparable in most ways with Rings of Power as Gandalf meant in the context of his conversation with Frodo.” (Inziladun).
  
• “all the ‘Rings of Power’ were forged based on some sort of design contrived by Sauron and that Sauron himself had a hand in the forging of the One and all the others, except the Three which Celebrimbor himself made. Even though Sauron had no hand in the forging of the Three it still had his imprint in design. I think therefore all of the other Rings, like the One, would have the same or similar effects on mortals, excluding the Dwarves. The Three, however, not so much but they were linked to the One based on their design so that they could all in some manner control the bearers through Sauron wielding the One.” (Belegorn).
  
  That sounds remarkably like a “back door” or “Trojan” computer malware, doesn’t it?
  .
• “Thrór was able to pass on his Ring because he was a Dwarf and not a Man” (Zigûr).
  
• “Gandalf was hyperbolizing” (Kuruharan).
  
  C.f., in the 2005 edition of Reader’s Companion, for p 499 regarding Treebeard as “eldest”, Hammond and Scull quote “Christopher Tolkien’s comment that his father was given to ‘rhetorical superlatives’, such as ‘the oldest living thing’”.
  JRR Tolkien was indeed given to ‘rhetorical superlatives’; we should not be surprised if Gandalf was, too.
  
• “Gandalf was giving Frodo a simplified version, leaving out unnecessary details” (Nerwen).

I’ll add a few other points, just to feed fuel to the fire.

• The Dwarves claimed Celebrimbor gave the greatest of the Seven to his friend Durin III. Later the Elves doubted it; but I’ll bet it’s true. Celebrimbor knew he was in trouble and needed to hide the Rings: he wisely sent the Three out of Eregion altogether. Perhaps because he gave the best of the Seven to Durin, Sauron was inspired to give the other six to Dwarves as well; and then the Nine to Men, who proved easier to ensnare.
• I think Gandalf was attempting to impress upon Frodo the power of a Great Ring, especially upon Mortals and in particular upon Hobbits: that Bilbo could give it up, albeit with a mighty big assist from Gandalf, who acted in this case as ἄγγελος, or angel, to overcome the power of the One Ring, something that perhaps Bilbo on his own could not do. In this regard, Tolkien wrote to Michael Straight, editor of New Republic in Letter 181,

  [Gandalf's] function as a “wizard” is an angelos or messenger from the Valar or Rulers: to assist the rational creatures of Middle-earth to resist Sauron, a power too great for them unaided.

  You are of course free to believe that Bilbo gave up the One Ring entirely upon his own or only with the assistance of Gandalf; I am inclined to believe it was only with the assistance of Gandalf. Frodo was later unable to give it up; Sam Gamgee did surrender it, willingly, to Frodo: but this was due in large part, I think, to his loyalty to Frodo, and to his simplicity of spirit: In that simplicity of spirit, he saw through the deceptions of the Ring when it tempted him to become “Samwise the Strong”, a test Boromir failed without ever wearing the Ring, a test with which Galadriel struggled even after millennia of contemplation and introspection.
• The Rings were never meant for Mortals in the first place. The Noldor of Eregion were trying to hold back the effects of time. Mortals turned invisible when they wore the Rings; I argue there is no reason to believe Elves did, but every good reason to believe they did not.
  • Tolkien himself tells us the Seven did not render Dwarves invisible or give them longer lives.
  • The Three certainly did not convey invisibility: Gandalf, Elrond, and Galadriel were all visible, and we know Galadriel was wearing Nenya at the Mirror of Galadriel.
  • The Elves wanted to stop the process of fading, whereby their bodies (hröar) were consumed by their spirits (fëar). If the Noldor were trying to prevent fading, why in blue blazes would they invent a device to make them invisible? The two goals are contradictory, at cross-purposes with one another.
  • However, Sauron’s methods apparently entailed some sort of necromancy. (He was, after all, The Necromancer.) If the Noldor under Sauron’s tutelage used necromantic techniques to accomplish their goals, then the Rings were drawing on the power of the Unseen, but in a most unwholesome way (excepting the Three).
    
    Men, though, including Hobbits, might be easily overwhelmed, and instead of “tapping” into the power of the Unseen, move altogether into the Other Side, which they perceived as a wraith-world because they entered it by means of necromancy.

Gandalf must explain all this quickly and decisively to Frodo, keeping in mind that his goal from the start is to convince him, above all, do not put on the Ring. Bear in mind also that he cannot say, “O, by the way, I have Narya, one of the Three, and here are some Ring-bearer tips you should know…” No, no! he’s going to scare the pants off Frodo! A little after telling him, “It may slip off treacherously, but its keeper never abandons it,” Frodo blurts out, “O Gandalf, best of friends, what am I to do?” Frodo is panicked! “You are wise and powerful. Will you not take the Ring?” And Gandalf can not take the Ring: it’s too dangerous for him. We would say, Frodo doesn’t know how to “turn it on”: he isn’t powerful enough to use it; for Gandalf, it’s a deadly trap. Poor old Frodo has the Radioactive Potato.

Finally, Frodo says, “…I must keep the Ring and guard it, at least for the present, whatever it may do to me.” This is exactly what Gandalf wants! And the wizard replies, “Whatever it may do, it will be slow, slow to evil, if you keep it with that purpose.”

So he didn’t give Frodo all the details. All the better. Ever read a contract? An End User License Agreement? “The party of the first will accede to the party of the second, except at the aforementioned times and in those places enumerated in Addendum C-2…” Frodo didn’t need the details. He needed to know that he was, in effect, living with the nuclear football hanging around his neck, and it had a (fortunately slightly defective) homing device.