1)
Why did he say Amod (masculine)?
1.
Rashi #1: Be zealous like a male to do so.
2.
Rashi #2: This is like La'amod (Radak -an infinitive), in place of a command (Malbim).
2)
Why did he say "if they will ask if there is a man here"?
1.
Malbim: It is improper to enter a woman's house when there is no man there.
1
When you say that no man is here, no stranger will enter.
2
1
Even if it is not forbidden due to seclusion when her husband is in the city (Kidushin 81a), it is improper. (PF)
2
I.e. even if they do not trust you and suspect lest I am here, amidst Safek they will not enter to check if they think that you are alone. (PF)
