1. Wine, over which we recite the Kiddush, can be a negative thing if used improperly. For example, according to some opinions the fruit of Adam’s sin was wine. This sin brought death into the world. Also, wine is used in a negative context as a sedative device before a person is executed.

So when we are about to recite the kiddush over wine, the reader says, Attention gentelemen—meaning to ask: Is this wine the wine of life or that of death?

And everyone responds: Lechaim! Meaning to say, this is the wine of life. We are using this wine for a holy purpose, to make kiddush. (Note: Some do not have the custom to respond with “Lechaim.”)

Everyone responds: Lechaim! Meaning to say, this is the wine of life. We are using this wine for a holy purpose, to make kiddush

3. In the olden days, when they would drink wine in middle of a meal, one person would recite the blessing while everyone else just listened and recited Amen. Then everyone could drink the wine.

The one reciting the blessing would say “Attention gentlemen” so that everyone would stop eating and talking so that they could listen to the blessing and say Amen. It therefore became the custom that every time we make a blessing on wine, even for kiddush and Havdalah, we preface it with Attention gentlemen.

4. From a Kabbalistic perspective, these two extra words are inserted in order to bring the total amount of words in the kiddush to a specific number that has kabbalistic significance (The Rebbe’s Haggadah).

Source: The Rebbe’s Haggadah citing Avudraham (Abudraham).