Kipling is trying to persuade us that we need to behave in certain ways and have certain character traits.  He is saying that we can only be true "men" if we act in these ways and have these traits.

Mainly, he thinks that we need to be confident and strong, believing in ourselves and never giving up.  You can see that in many quotes, for example:

IF you can keep your head when all about you
Are losing theirs and blaming it on you

And

If you can force your heart and nerve and sinew
To serve your turn long after they are gone,
And so hold on when there is nothing in you
Except the Will which says to them: 'Hold on!'

I agree that these qualities are admirable.  I do think that it is important to be calm in tough circumstances.  I agree that it is important to never give up and to have a strong will.  I do not agree with Kipling's belief in the supremacy of the white male, but it is not explicit in this poem anyway.