The whole sentence means that it is good to set up the lofty ideal of "ruling the country and leveling the world", but to achieve the goal, we must cultivate self-cultivation, constantly cultivate self-cultivation, cultivate the mind from the outside, and constantly cultivate self-cultivation. To practice outside is to always pay attention to your words and deeds when you are outside. There must be a teacher in a threesome, and no one is perfect. See the advantages of others and learn from them. If a person's words and deeds are really charming from the inside out, then this person's cultivation is definitely the peak.
To cultivate one's mind and keep one's word is to keep it in mind and follow the regulations.