I adhere to the old saying that "he who refuses to learn from the past is doomed to repeat it." Recognizing mistakes--or, for that matter, learning from positive examples of historical significance--should be an important factor in decision-making for future generations. Events of the past, instead of being something to disregard, should be studied and considered carefully; future events can be altered and disastrous repeats avoided by the knowledge gained of prior events.

The actual quote by George Santayana was "Those who cannot remember the past are doomed to repeat it." 

However, I agree with everything else you've said.  Especially in light of disturbing parallels between what is happening today and what happened 80 years ago. 

My own personal past is important in that medical questions which may affect my children must be remembered and considered in the decisions which they make.  My ancestral past is important in knowing why my ancestors made the decisions they did such as why did they leave the country of their birth?  Why or how did they successfully mix religions and ethnic origins when so many cannot? How did the medical mysteries of the brain come to affect my ancestors and my own family so greatly?  Without knowing any of my history, I would not have been able to make some of the positive decisions I made.  Yes, I made mistakes and tried to prevent my family from making the same mistakes. For the same reason knowing your own history is important, so is knowing the history of other people in other countries or cultures.  The world is becoming a smaller place with travel introducing many people to ours or other cultures for which we need to be prepared.  For example, since my children became adults, in my birth family, we now have  wonderful men from Africa and South America, wonderful women from Southeast Asia, religions which include Christian, Muslim and Buddhists, and skin colors of all beautiful shades.  Knowing history helps our whole family know that history impacts us all on both sides of the interaction.

The past cannot be ignored because it influences the present.  On a personal level, your past makes you who you are.  The same is true on a cultural level for a people.  A people's shared past is part of their shared culture.  It is what makes them unique.  It is what makes them who they are.

The past shapes the present. In this fact, simple but significant, we can see why the past is important. In an ordered sequence that goes from A to B to C, we can see that the nature of the entire sequence changes when one letter is removed. Also, there would be no "C" without a "B" before it. 

The present relies upon the past to become what it is. This is true for individuals and nations. 

One example of a practical implication of this idea can be found in parenting. If a person would like her child to grow up to be similar to her, she will need to provide similar childhood experiences for that child. She will need to have knowledge of her personal history if she wants to repeat that history for her child.

I adhere to the old saying that "he who refuses to learn from the past is doomed to repeat it." Recognizing mistakes--or, for that matter, learning from positive examples of historical significance--should be an important factor in decision-making for future generations. Events of the past, instead of being something to disregard, should be studied and considered carefully; future events can be altered and disastrous repeats avoided by the knowledge gained of prior events.

I find it intriguing that the question asks why "the past" is important rather than why "history" is important. Things that happened in the past have ramifications that we can still see today. Slavery, for instance, has a legacy in many rural areas throughout the South, where I live. There are countless other examples. Many nations around the world confront the problems created by longstanding tensions between ethnic groups. Government policies in the past contributed to the economic meltdown in 2008. The aftereffects of imperialism still resonate in many countries. This fact is what makes history so important. History, of course, is the discipline that tries to make sense of the past. 

Hopefully we as individuals, and we as a country can learn from what we have done in the past.  For example, if the country has gotten into one war like Vietnam where we were trying to achieve a non-military purpose through military means, we will know enough to avoid getting caught up in that same kind of mistake again.  Of course, this is easier said than done both for countries and for individuals.