It means that in order to advance or step into a better future we need to know the basis/grounds or history of our past. We cannot advance in the future if we do not have a knowledge about our past or our origin.

For example : If someone wants to come out with a better type of a car, the person needs to know about the history of car making and how it started in order to avoid the mistakes that have already been committed and to learn and gain experience from those mistakes and developments.

Hope it is clear now

One must understand what has happened and learn from it. This way, bad situations are not repeated in the future.

and yes, i would replace we with one.