Halavai, or vlavai is a talmudic expression used colloquially in frum circles and by secular Israelis to mean if only or would that it were so. One might say it feelingly as in halavai, that he should meet a nice Jewish girl, or wistfully as in halavai, that I could spend more time learning Torah or, ironically, as in halavai, that we should all be so clever.
Halavai comes from the word lu (spelled lamed vav) meaning may it be so. (Remember the campfire song by Naomi Shemer Lu Yehi?)
Lu first appears in the Bible when God promises Abraham that his wife Sarah will bear him a son, and an incredulous Abraham can only reply, Lu Yishmael yihyeh lfanecha, Would that Yishmael (Abrahams son by Hagar) should live before you (Genesis 17:18.)
The most poignant vlavai in the Talmud occurs in Berachot 28b. Rabbi Yochanan Ben Zakkai is on his death bed. His students ask him to bless them. He responds: May it be His will that the fear of heaven should be upon you like the fear of flesh and blood.
The students are not impressed. Only that much? they ask. Surely a respectable blessing would be for the fear of heaven to far surpass their fear of human beings?
Vlavai that it was that much, answers the rabbi. For know that when a person sins, he says let no man see me. Would that we cared as much about what God thinks as about what other people think, is Rabbi Yochanan Ben Zakkais blessing to his students.