Poems can mean any number of things, of course, and I'm a skeptic when it comes to us trying to say with any certainty what an author intends for us to understand. Yet, still, I'll gladly try my hand at offering an answer.
The thing that strikes me first about David Ignatow’s poem "The Bagel" is that there a cyclical movement combined with some sort of change. The clearest sign of this combination of return and transformation is seen in the poem’s opening and closing lines. In lines 3-4, the speaker is “annoyed with myself / for having dropped it,” with the “it” referring, of course, to the lost bagel. By the end of the poem, in line 13, the speaker is now “strangely happy with myself.” At its end, then, the poem returns to nearly the exact string words from the opening of the poem – only the adjective has changed here: “annoyed” has become “strangely happy.”
Diction and symbolism in the poem may also be tied to this combination of return and transformation, especially if diction can be said to include sentence structure. The poem consists of only two sentences. The second sentence seems to me to be full of a sort of grammatical or syntactical tumbling; it moves forward, but it does so much more in a non-linear fashion than, say, in the way that the first sentence sets the stage. Symbolism may be even easier to find in the poem. The bagel is round, so it can roll away, and the speaker begins to roll, too, by the poem’s end.
As for the poem’s ultimate meaning, though, the best I can do if offer a sort of Beat Buddhist approach, one in which an individual celebrates gaining awareness and, at times, losing a little bit of what we might see as sanity (the poem celebrates the “strangely happy”). In this Beat Buddhist approach, the speaker may be seen as abandoning the pursuit of things (the bagel could symbolize any sort of earthly thing that we chase after: money, love, power, or whatever) and, in so doing, is liberated from the grueling nature of the chase itself. The enotes link below confirms Ignatow’s connect to Allen Ginsberg and the other Beat poets, who were steeped in their own versions of Buddhism, so my reading may have some merit to it.
Don’t think that this answer is the only possible answer. Maybe you have come up with something very different.