Gemara: That which [Yirmiya lamented], "My spirit was deprived of peace" (Eicha 3:17), is referring to [the inability to light] Shabbat candles.
Ein Ayah: Daytime is set aside for lively human interaction, whether or not a person tends to enjoy being around other people. However, night is the time when one retreats to his natural surroundings. If he is one whose love of peace is well-entrenched in his soul, because he and others relate to each other properly, then he will benefit from continuing interaction and will want to make night day-like. Such a person will consciously decide to light candles, so that he can enjoy seeing those close to him.
During the week, when people are used to working and toiling, a person will not always focus on his internal life. He will be forced into working hard during the day and resting up at night for the next day’s toil. On Shabbat, the feelings of the heart return to act as they naturally do, and one feels the natural enjoyment of life. If he finds at that time that the people who surround him make him feel good and loved, then he will easily appreciate the need to have light even at night so that he can take the choice to pursue the relationships. That is different from the relationships he has during weekdays, because those are relationships of necessity and these are relationships of choice.
However, when the world becomes a dark place for the nation and enemies afflict its members, people around a person are often a bitter yoke, as happen to people whose lives are out of order. Then, when he has a desire to cling to his internal life on Shabbat, he will, for the most part, choose isolation, as opposed to the task of interacting well with others. A depressed person will look negatively at relationships and be deprived of peace. This is different from the time of national tranquility, when things around a person were upbeat, as he would feel a desire to have Shabbat candles to broaden the social opportunities by choice. But after the exile, when we are among people who are foreign to us, society is a source of pain and hatred, and a person prefers to avoid the attempt of peaceful interaction but to look within his inner spirit in solitude. It allows him to escape from the society that forces itself upon him during the day.
The above is what a person would feel were the Rabbis not to have lit our path in the way of Torah and mitzvot. Shabbat is a special present which is connected to the divine promise that we will have an era of tranquility in which the nations will treat us with respect. Then we will be interested in embracing relationships, and this spirit will extend to the whole world. So even if Israel will call out its desire to forget about the light of the Shabbat candles, while we are in the depths of the darkness of exile, Hashem’s word will counteract our inclination and will restore our spirit. Hashem’s impact on us through the medium of mitzvot will "skip over mountains" and lift us to the heights of the future, to the time of the kingdom of Mashiach. That is why we are commanded to light Shabbat candles and thereby reawaken the pursuit of positive relationships, for "Hashem will not deprive forever" (Eicha 3:31), as he is the Master of Peace.