Who you ARE was what you WERE. In other words, your past self determine your current self. And your current determine the future you.
For instance, you studied medicine (in the past) and am a doctor today. You are a doctor today because you studied medicine. In future you become a specialist because you work towards being one today.
Another example is savings. How much safety net you have now, depends on how much you have saved and grew your money in the past.
If we protect the environment today, the world will be a better place to live in tomorrow. Similarly, if we use resources indiscriminately, and produce loads of greenhouse gases, then the world will not be as great a place to live in in future.
For quite some time in the past, I had been cruising. I have a job, and am doing what I need to keep it....