"If" is basically an instruction manual for how to be "a man," at least according to the speaker. It is basically 30 lines of "if you do this, and if you don't do that," followed by two lines at the end that explain everything. Yes, you have to wait until the very end to find out what will happen if you do the following: keep your head, don't lie and hate, risk everything and lose it but start over again, watch everything you've dedicated yourself to get destroyed but then bend down and rebuild it again, handle success and failure with grace, don't get too upset if people twist your words and use them to deceive people and… that's the gist of it. If you can do all this, the speaker says, you will be a man, and will have the world and everything in it. So, you'll have that going for you.