What is the context and nature of Portia's remark about a mocker in The Merchant of Venice?

At the beginning of Act 1 scene 2, we are introduced to Portia and her handmaiden, Nerissa, who is also a friend and confidante, who are in conversation about Portia's deceased father's decision to will that his daughter's future spouse should be the result of a lottery that he has devised. Portia is quite upset about the arrangement since she has no choice in the matter but has decided to respect her father's wishes lest she forfeit her inheritance.

Since Portia is about to inherit considerable wealth and is beautiful and intelligent to boot, the lottery has encouraged many suitors to come to Belmont and try their luck. The situation at this point is that no less than six suitors have arrived. Portia has obviously met and conversed with them and has formulated an opinion about each. During their discussion, Nerissa asks her:

But what 
warmth is there in your affection towards any of 
these princely suitors that are already come?

Portia then proceeds to describe each suitor. In all instances, she seems to be quite cynical and points out each gentleman's negative traits. The reference to 'mocker' is made when Nerissa asks her about the French Lord, Monsieur Le Bon. Portia responds:

God made him, and therefore let him pass for a man. 
In truth, I know it is a sin to be a mocker: but, 
he! why, he hath a horse better than the 
Neapolitan's, a better bad habit of frowning than 
the Count Palatine; he is every man in no man; if a 
throstle sing, he falls straight a capering: he will 
fence with his own shadow: if I should marry him, I 
should marry twenty husbands. If he would despise me 
I would forgive him, for if he love me to madness, I 
shall never requite him.

It is evident that Portia does not like the lord much and questions his manliness, conceding only that since he has been created as a man, she has to accept him as such. She acknowledges that it is sinful to 'to be a mocker,' that is, to make fun of others (a possible indication of deeply entrenched religious values), but says that the monsieur displays such silly behavior that she cannot help herself.

Portia's speech indicates that the lord was showing off for her so much—fencing 'with his own shadow' and dancing at the sound of a bird's song—that she wasn't able to get a sense of who he really is—'he is every man in no man.'

Portia expresses concern that if she should be compelled via the lottery to marry him, she would have her hands full. She is also frank about the fact that even if he should love her madly, it would be impossible for her to return his affection.