How does Marlow describe the parially completed report that Kurtz penned before lapsing into his fatal illness? What effect does that report have on Marlow?

From the text:

".....I had had two rows with the manager on the subject out there. I had refused to give up the smallest scrap out of that package, and I took the same attitude with the spectacled man. He became darkly menacing at last, and with much heat argued that the Company had the right to every bit of information about its 'territories.' And said he, 'Mr. Kurtz's knowledge of unexplored regions must have been necessarily extensive and peculiar -- owing to his great abilities and to the deplorable circumstances in which he had been placed: therefore -- ' I assured him Mr. Kurtz's knowledge, however extensive, did not bear upon the problems of commerce or administration. He invoked then the name of science. 'It would be an incalculable loss if,' etc., etc. I offered him the report on the 'Suppression of Savage Customs,' with the postscriptum torn off. He took it up eagerly, but ended by sniffing at it with an air of contempt. 'This is not what we had a right to expect,' he remarked. 'Expect nothing else,' I said. 'There are only private letters.' He withdrew upon some threat of legal proceedings, and I saw him no more; but another

fellow, calling himself Kurtz's cousin, appeared two days later, and was anxious to hear all the details about his dear relative's last moments. Incidentally he gave me to understand that Kurtz had been essentially a great musician. 'There was the making of an immense success,' said the man, who was an organist, I believe, with lank grey hair flowing over a greasy coat-collar. I had no reason to doubt his statement; and to this day I am unable to say what was Kurtz's profession, whether he ever had any -- which was the greatest of his talents. I had taken him for a painter who wrote for the papers, or else for a journalist who could paint -- but even the cousin (who took snuff during the interview) could not tell me what he had been -- exactly. He was a universal genius -- on that point I agreed with the old chap, who thereupon blew his nose noisily into a large cotton handkerchief and withdrew in senile agitation, bearing off some family letters and memoranda without importance. Ultimately a journalist anxious to know something of the fate of his 'dear colleague' turned up. This visitor informed me Kurtz's proper sphere ought to have been politics 'on the popular side.' He had furry straight eyebrows, bristly hair cropped short, an eyeglass on a broad ribbon, and, becoming expansive, confessed his opinion that Kurtz really couldn't write a bit -- 'but heavens! how that man could talk. He electrified large meetings. He had faith -- don't you see? -- he had the faith. He could get himself to believe anything -- anything. He would have been a splendid leader of an extreme party.' 'What party?' I asked. 'Any party,' answered the other. 'He was an -- an -- extremist.' Did I not think so? I assented. Did I know, he asked, with a sudden flash of curiosity, 'what it was that had induced him to go out there?' 'Yes,' said I, and forthwith handed him the famous Report for publication, if he thought fit. He glanced through it hurriedly, mumbling all the time, judged 'it would do,' and took himself off with this plunder."