Why is Jessica considered better than Shylock in The Merchant of Venice? She stole his money, took and sold her father's ring that he kept for sentimental rather than monetary value because it was given to him by his wife before they married. Is she considered better than Shylock because she wanted and did become Christian through her marriage to Lorenzo?
This is a very interesting question and it is possible that the answer lies with understanding Antonio. The Renaissance world was singularly divided between Christian and Jew. In some places, Jews were expelled. In some, Jews were forced to convert to Christianity or expelled if they would not. In some, as in Venice, Jews were forced to convert as punishment for crimes. Antonio and Shylock together illustrate some of the tensions and dissension existing between Christian and Jew at the time. Reflecting this milieu, you are certainly correct in saying that, the Christian characters value Jessica, whereas they do not value Shylock, because she converted to Christianity.
Shylock and Antonio are major antagonists to each other. Antonio is immediately established by Shakespeare as a liar and as a reckless man (at least somewhat reckless as we don't know the extent of habitual nature of his recklessness). In a very surprising move, Shakespeare has Antonio tell Salarino and Salanio that he is not anxious about the fate of his ships because he is not foolish enough to invest all his wealth in one merchandising venture. He almost immediately thereafter says to Bassanio that he can not help him with his financial hope because he has put all his capital in the ships that he is waiting for (the exact opposite of what he just told the others).
Believe me, no: I thank my fortune for it,
My ventures are not in one bottom trusted,
Nor to one place; nor is my whole estate
Upon the fortune of this present year:
* * * * * * * * * * * * * *
'Tis not unknown to you, Antonio,
How much I have disabled mine estate,
Thou know'st that all my fortunes are at sea;
Neither have I money nor commodity
To raise a present sum:
Shakespeare makes Antonio a liar. Does he also thereby make him an unreliable character so that his opinions of Jessica and Shylock are subject to suspicion or even rejection by his Renaissance audience?
Shakespeare shows the antagonism between Shylock and Antonio with a long history that Shylock alludes to of public abuses leveled at him by Antonio and of Antonio's attempts to interfere with Shylock's business. In doing, does Shakespeare intend to cast Antonio as the defender of right or to cast him as the persecutor of innocent persons?
[Aside] How like a fawning publican he looks!
He hates our sacred nation, and he rails,
Even there where merchants most do congregate,
On me, my bargains and my well-won thrift,...
Jessica's reasons for leaving her father's house and stealing what he holds dear are simple: she loves the Christian Lorenzo; she wants to wed Lorenzo and needs wealth to do it; she is required by law to convert to Christianity to wed the Christian Lorenzo; her father forbids her (or would forbid if she ever asked him) to wed a Christian and in doing so renounce her Jewishness; her father would decline to provide wealth to her for such renunciation and such a marriage.
Alack, what heinous sin is it in me
To be ashamed to be my father's child!
But though I am a daughter to his blood,
I am not to his manners. O Lorenzo,
If thou keep promise, I shall end this strife,
Become a Christian and thy loving wife.
So the question is, while Jessica is favored by the Christians in the play for her conversion, is Shakespeare actually calling to account the attitudes and beliefs that value her above Shylock by showing the impurities in the protagonist's, Antonio's, inner character? If this is what Shakespeare is aiming at, then Jessica is not really intended to be valued above Shylock, but the audience is meant to question everything the Christians, headed by Antonio, believe and value about Jews and about Shylock who, yes, behaves grievously yet not without manifold provocations.