Straight from planning of killing Duncan, Lady Macbeth is trying to get Macbeth to go commit to kill Duncan. However, Macbeth is almost instantly objects to it and really does not want to go through it. Lady Macbeth call him a coward and says he has no manhood for not wanting to kill Duncan. Example of which is when Lady Macbeth tells herself that she can murder Duncan and says “ come you spirts, that tend on mortal thoughts, unsex me here”
If this happened to her, she would not be bothered by a women’s kindness, she would be a killer, like a man. When
Macbeth had his soliloquy, after Lady Macbeth called him a coward and lack of manhood. Macbeth was stating on how he did not want to kill Duncan, because he is loyal to Duncan and he could never betray him. He states that he is supposed to protect Duncan, and if needed give his life to protect him. This to me shows manhood that Macbeth shows.
Finally, to me in Macbeth, what shows manhood is the quote he says “If it were done quickly” I feel he is saying that if he were to kill Duncan he would want to make his death fast and not a slow and painful one even if it is murder, a true man would want it to be a quick one.
Following that quote, he does know that if he kills Duncan he will have to resolve the entire thing and own up to it all. Otherwise he would be risking his soul to not get into the afterlife. I think that he is showing his manhood, that he would need to resolve the killing.