It feels like a lifetime has passed, and I feel grateful for the past and present, but I have no idea what it means.

It means that they seem to be separated by a lifetime.

It is often used to describe feelings about the changes in time and the great changes in things.

The idiom comes from the second volume of "Wu Chuanlu" written by Fan Chengda of the Song Dynasty, "Founded in Changzhou. Relatives from Pingjiang who came to meet each other in the past came to each other one after another, and they suddenly seemed to be separated from each other." To make a sentence out of the idiom, many lonely elderly people who have lived in Pudong for a long time, following the "See the New Face of Pudong" activity organized by the neighborhood committee, saw the newly erected new buildings and the bridges on both sides of the bank. Many people lamented that in just three years, But it felt like a world away.