Kipling's poem "If" is a message to a young man dictating how he ought to live his life if he wants to be successful. There seem to be two main aspects to the speaker's opinion about how a man should live.
The first aspect is that a man should always be persistent and never give up: this is most evident in the lines, "[If you can] watch the things you gave your life to broken, / And stoop and build 'em up with wornout tools." However, Kipling uses the syntax of the poem to drive home this message further: each new instance of "if" is a new clause to a very long sentence that only is completed with the last two lines of the poem (i.e., the poem is a very long sentence). As a result, just like the young man must never quit in life, the reader must also never quit in reading to discover the final thought.
The second aspect that the speaker advises is that the young man should value moderation, and never go to extremes, as in the lines, ""If you can dream - and not make dreams your master; / If you can think - and not make thoughts your aim." The young man should value dreams, but shouldn't be ruled by them, expressing moderation. Kipling uses form to highlight this message in the poem: though the poem is divided into four stanzas of eight lines, the stanzas seem to come in "units" of two lines each. For example, the lines, "If you can keep your head when all about you / Are losing theirs and blaming it on you," are a complete thought and are bound together syntactically, while the lines "If you can talk with crowds and keep your virtue, / Or walk with kings - nor lose the common touch," both reference walking and are bound together thematically, and finally, the aforementioned lines about dreaming and thinking are bound together by a parallel structure. By balancing his lines in sets of two, Kipling suggests that the young man should also balance his passions and interests to lie between two extremes.