a) Through the joy of Shabbat a Jew merits to liberty and then the mind is perfected and he is not confused. By this he merits to fear of G-d with understanding, without any foolishness. And he raises all the fallen (material) fears so that he will have no fear of any material thing- not from any minister or lord etc. rather he will only fear G-d alone.
b) A Jew has to be very careful indeed to be happy and of good heart on Shabbat. For the virtue and holiness of Shabbat is very great and very precious, as clarified in all the holy books, especially in the book 'Reishit Chochma' in the beginning of the chapter 'The Gateway of Holiness'. It is fitting to learn this chapter and take to heart well all the things said there about the tremendous virtue of the holiness of Shabbat in order that one's heart will be enthused to receive Shabbat with tremendously great joy, for the essence of the commandment of honouring the holy Shabbat is the joy, meaning to be very happy on the holy Shabbat without showing, Heaven forbid, any sadness or worry at all on Shabbat. A Jew has to maximize the delights of Shabbat with all kinds of delight, whether eating, drinking or clothing, as much as he can, for the eating on Shabbat is entirely holy, entirely spiritual, complete Godliness; it rises to another place altogether from the weekday eating. Happy is he who strives to be happy on Shabbat, for the main way to honour Shabbat is with joy, as explained above.
c) It is the way of G-d to look at all the good things that we do even though they also contain bad elements; He doesn't look at this . Even more so, a Jew mustn't look at his fellow negatively by finding in him specifically things that are not good or looking for and finding in his fellow blemishes in his service of G-d. On the contrary, he must look only for the good.