The poem's content concerns a father defining for his son the qualities of a good man and a leader. He is setting the parameters or boundaries for his son and giving him goals to achieve. The poem deals with life's challenges and how to deal with them.
Stanza one discusses being confident about the decisions you make and taking responsibility for those decisions. If others, who cannot take that responsibility for themselves, react negatively to what you have decided, you should be patient with them and not reduce yourself to their level by telling lies or dealing in hate. However,
"...don't look too good, nor talk too wise" (line 8)
Don't ever believe you are above someone else.
Stanza two applauds dreaming but warns not to let your dreams control your life. Thinking is also praised, but Kipling warns that it does no good to think if you don't put those thoughts into action. Everyone experiences success and disaster in life, but it is important not to take them too seriously because they are not the substance of life; they are the extremes. If you hear things you said misquoted or misstated or see things you have done destroyed, you need to
"....stoop and build them up with wornout tools." (line 16)
Pick yourself up and rebuild with everything that you have left in you.
Stanza Three counsels not to fear taking risks and possibly losing everything. If you do lose everything, don't dwell on it or talk about it all the time, just start over at the beginning. When you are tired and exhausted and your body feels like it can't continue on, use your mind and your will to command yourself to
"Hold on" (line 24)
Persevere. Push through it.
Stanza Four concerns the treatment of others. You need to be able to talk to large groups of people and yet not let them influence your belief in what is right, wrong, moral, or immoral. You need to be able to walk with men of power and influence and yet not forget the common man and his needs. You need to know yourself and your beliefs so well that neither your friends nor your enemies can hurt you because you know who you are and what you stand for. People can depend on you, but don't let them become too dependent on you. You need to live every single minute of your life to the fullest. If you do these things,
"Yours is the Earth and everything that's in it,
And - which is more - you'll be a Man my son!" (lines 31-32)