What is the effectiveness and impact of the different poetic devices used in "IF" by Rudyard Kipling.

1) Personification is when inanimate objects are spoken
about as if they were human.  For example, the following sentence uses personification:
The sun was smiling on the children in the park.

"If" is
not very rich in personification.  The only example I can find
is:

And so
hold on when there is nothing in you
Except the Will which says to them:
"Hold on";

In this passage, a
person's "will" is pictured as a living being that can "talk" and say, "Hold
on." 

2) Alliteration is the repetition of beginning
consonant sounds.  Some examples from "If" are:

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"treat those two
impostors";

"the truth you've spoken/Twisted by knaves to
make a trap for fools";

"sinew/To serve your turn.../And so
hold on..."

These examples of
alliteration, and others, serve to draw the reader's attention to certain key phrases. 
In the second passage, for example, alliteration draws our attention to some of the
opposing forces that the poem discusses: truth, and traps.

3)
Metaphors are comparisons that do not use the words "like" or "as."  This poem speaks
mostly in straightforward language; still, it does contain some metaphors, such
as:

"triumph
and disaster...those two impostors"';

"the truth.../Twisted
by knaves to make a trap for fools" (truth is compared to a metal object that can be
twisted out of
shape).

Metaphors such as
these make the poem much more beautiful and memorable.  Imagine if Kipling had written:
If you can bear to hear the truth you've spoken misrepresented by knaves in such a way
that they would cause fools to make intellectual errors.  Not exactly
memorable!

4) By far the most important device used in this
poem is the repetition of similar words or phrases; this is referred to as
anaphora. 

Consider these examples  just from the first
stanza:

when
all men DOUBT you,/But make allowance for their
DOUBTING;

If you can WAIT and not be tired by
WAITING;

Or, being LIED about, don't deal in
LIES;

Or, being HATED, don't give way to
HATING.

These repetitions
serve to emphasis one of the poem's major themes: balance.  Kipling believes that many
character traits and actions must be used, but always in the proper
balance.

You must wait sometimes, but not become worn out
by waiting. You must be decisive, but not so cocksure that you cannot "make allowance"
for others who doubt.  You must dream, but not be enslaved to your dreams; you must
think, but "not make thoughts your aim."