This custom is a means of overcoming a Halachic dilemma. Women light Shabbat candles prior to the onset of Shabbat on Friday.The general rule is that once a woman recites the blessing of “L’hadlik ner shel Shabbat-(to kindle the light [candle] of Shabbat.) she automatically assumes all the positive as well as the restrictions of Shabbat. Accordingly, at that moment she is no longer able to hold a candle or to light her Shabbat candlelabra . To simply light the Shabbat candles first and then to recite the blessing would violate the general rule that blessings precede the performance of a Mitzvah( a Biblical or Rabbinic mandated action) To offset this problem the custom developed to first light the Shabbat candles. The women then close their eyes and only open them upon the conclusion of the blessing. Thus the women do not violate the Shabbat by actually lighting the Shabbat lights after the blessing. By opening their eyes after the blessing they are symbolically manifesting that they are enjoying the light only after the blessing as is the general custom of blessings.
The rabbis of the Talmud teach that one is to say 100 blessings a day. That means 100 times a day we are to stop, take a breath and notice that divinity is present at every moment. Traditionally some of those blessings are imbedded in the daily prayer services. Others of the blessings are for moments of gratitude, before we eat, for example, or when we use the bathroom and recognize how lucky we are that are bodies are working. Still others of the blessings connect us to commandments, those actions in the world our tradition teaches God expects of us. We say:”Baruch Ata Adonai, Eloheynu melech ha-olam, asher kidshanu b’mitzvotv vtzivanu …fill in the blanks.” The root of mitzvot means “commandment”, and some would argue that it might also mean ‘connection.’ So I choose to translate the familiar blessing form in this way: “Holy One of blessing, whose presence fills creation, you make us holy through connections, and connect us to each other and to you through….fill in the blanks.” And then we do the action we just named…. affix a mezuzah, wrap ourselves in tzizzit as we put on a tallit, light a candle of Hanukah.