"If" is a laundry list of admirable qualities for masculinity and manhood. Particularly important in the poem is the line about "...if you can keep your head while all about you others are losing theirs (paraphrase)."
Kipling here is basically giving sound advice to his reading audience in regards to life. Stay calm, be cool, and strive for excellence. By doing so, he is establishing himself as a bit of an amateur philosopher.
The advice is sage and sound, but as previous posters have noted, perhaps a bit unrealistic in our current day and age. Such expectations were not unrealistic, however, in previous times and eras, when men were expected to "wear the pants" and so forth.
I believe the poem is trying to set the standard for what a "man" of Rudyard Kipling's time would be. The father's advice to his son is admirable, but unrealistic. One would have to be a super hero to achieve the status of manhood! Maybe that is the point, that being a man takes near perfection. I would hope that attaining some of these ideals would help the son onto the road of manhood and give him a goal for which to strive. Perhaps parents like to give advice to their children that they themselves did not achieve and regret bitterly as they grow older.
In the poem 'If' by Rudyard Kipling, the poet describes a recipe for becoming a man - the best of men - and a list of ingredients! One of the reasons that the poem may seem a little outdated today, and the advice a little too much of a tall order, is that lessons for men have changed because the roles of men have changed. In Kipling's day, the advice to 'keep your head' when others are losing theirs,for example, would have been achievable and highly relevant for a potential army officer! Nowadays, that potential recruit is very likely to be a girl. Also, men were expected to take charge, be leaders and show unsentimental 'backbone!' The lesson for them today is more likely to be to share in the diaper changing and cooking.