Oh, not the good parts of your past. It's important to remember your first crush from kindergarten, or the year you got the Barbie Dreamhouse. It's important to remember your algebra. (I guess. Of course, I never retained it for more than the time it took to take the tests. I'm close to 60 and I've lived pretty okay without it.) You want to remember the smell of your grandmother's apple cake, and the sound of lawnmowers on Saturday mornings. Good memories.
I mean the parts of your past that you hold onto that tie you down and impede your progress. The parts that keep you a Victim. The parts that show up in the midst of a good day, and remind you that you're really not worthy of that good day. Lousy memories. Memories of getting chosen last for kickball, or eating alone in the cafeteria, or having someone you love leave you. Those sort of memories don't help.
Unless. You take them and turn them around to change your behaviour.
If you've been chosen last at kickball, don't hoard that hurt; re-use that to challenge yourself to be the kind of person who watches for those on the sidelines and encourages them.
If you've eaten alone in the cafeteria, don't hoard that hurt; take your tray and find someone else who's eating alone.
If someone you love has left you, don't hoard that hurt; there are so very many ways to change that into positive and wonderful ways of reaching out to others, and also ways of being loving to yourself.
We all know people who hoard the past, who can't seem to get off dead center, who continue to define themselves by something or some one that caused them pain in the past. Don't be someone who hoards that hurt. Go read John 16:33. Go read 1 Peter 5:7. Then go clean house, and start letting go of the past so that your future can begin.