What do these pronouns indicate and ...?

I did not know Nehru at all intimately; in fact, I did not even meet him many times. But his personality made an immediate impression at one's first meeting with him,
and this impression did not change over the year. Nor was the effect he made just an impression; the word is weak and too cold. "Captivation" comes nearer to the truth.
Here was a human being who could win one's heart and keep it.
This would be something remarkable in anyone in any walk of life; but in someone whose position was humble and obscure it might not be so surprising as it was in a world-famous
statesman who has left a deep mark, and this on the whole world and not just on his own country. In this great statesman, the lovable human being was not smothered by the eminent public figure;
I should say that, in Nehru, there was not even fainest touch of pomposity or self-importance or self-consciousness. He retained the spontaneity and the buoyancy of youth after he had been
carrying for years an unusually heavy burden of office. It was not till his last years that the unforeseen breach between India and China began to bow him down under its weight.

1) The first pronoun 'this' and the second, third pronoun it in bold indicate 'being able to win one's heart and keep it'; Am I right?
2) The forth pronoun 'this' in bold indicate 'a deep mark'; Am I right?
3) Why is there a comma before the first underlined 'and' ?
4) Why is the second underlined 'and' used, not a comma?