"Lest we forget" is a very important phrase that means we should always remember something special or important. It can be used to remember people, events, or things that shaped our lives in some way.
Imagine you have a special toy that you love to play with every day. But, one day, you accidentally lose it and you can't find it no matter how hard you look. You start to forget about it and stop playing with other toys. However, your mom tells you "Lest we forget", reminding you to keep looking and not to forget about the toy.
In a bigger sense, "Lest we forget" is often used to remember people who fought for our country, especially during times of war. It helps us always remember their sacrifice, bravery and the importance of peace. It also reminds us to be thankful for what they have done and to make sure that we never forget their contribution to our society.