In the poem of Walt Whitman, [I celebrate myself, and sing myself], what do the last four lines mean? Thank you very much for your answer.
I believe you are referring the concluding lines of section one and not the entire poem (52 sections long) so I will comment on that aspect.
Those lines read:
Creeds and schools in abeyance,
Retiring back awhile sufficed at what they are, but never forgotten,
I harbor for good or bad, I permit to speak at every hazard,
Nature without check with original energy.
In the first line, Whitman is retiring dogma. "Creeds and schools," that is, the segmenting of thought and discipline, have been suspended for a time.
The second line says that he has not forgotten the lessons learned, but for now, they are only that...lessons, not living itself.
The third line recognizes that the speaker is going to speak his mind no matter what the personal cost. He will reveal in the sections that follow both the good and the bad about himself, come what may.
The fourth line sums up the whole section: "Nature without check and with original energy" realizes that nature without "check" can be wild, untamed. (Think of a mowed lawn vs. a meadow). The "original energy" is that in our nature that existed before the manicuring of our true, uninhibited selves.