Acceptance is about validating and saying hello to what is, that is, what is going on right now for you. With acceptance, you can clear the way to move forward spiritually. If you are in denial of a part of your reality, you will continue to be owned by that piece. Accepting what is, does not mean you are powerless to change your situation. It means, you are clear about where you are, and what you are working with. You are outside of judgment.
I watched a friend as he steadfastly denied the fact that he was dying of cancer. He explored numerous possibilities to turn his illness around and heal himself. In the process, he did a fair amount of healing, and was able to access some spiritual information as well. It was, however, only when he actually accepted the fact that he was going to die that he was able to really make significant shifts spiritually. At that point, his energy was released from the struggle, and became focused on his actual spiritual state in a body that was dying. Then, and only then, was he able to transcend many of his core issues. He was able to touch into Source, into pure love, in a way that he had never experienced before. If he had stayed in denial, and fought the reality of his illness to the end, he would not have been able to make this spiritual growth. He died well, with love, from a transcendent place. The night before his death, he repeated over and over again like a mantra: "love you, love you, love you". He had found the truth, that the core of Source is simply love.
Many people do spiritual work based purely on positive affirmations, without reference to, or acceptance of, their state at that moment. You can, if you so choose, create an entire alternate reality of all those positive places, but still the other reality remains. We can call it denial, or we can just call it not accepting what is. The important thing is being neutral with it, not judging it.
The power of being in a state of acceptance is knowing you can shift your reality at any time. You can create any future you want. You are a totally limitless spiritual being free to create anything you want. Heal the past. Transcend your karma. It is all possible. But right now, in this moment, you need to accept where you are, not viewing it as either positive or negative, but from a place of neutrality and love. Honesty with your state is key. It is so easy to be in denial, and to fool yourself into not being aware of your actual state because you believe that some part of your reality is not acceptable. It is far more important to know and to accept your state than it is to pretend that you are different. Can you look at the thing that is so unacceptable about yourself, and can you love it? Acceptance is about tuning into you as Spirit, the eternal, powerful being, and getting neutral and out of resistance. Look at what you're dealing with right now. Accept what is, and then work on what you want to change. In order for an addict to heal anything, he/she has to accept that he/she is, in fact, an addict. Acceptance frees up a tremendous amount of energy, and allows the healing to happen. You can heal the past, and you can create your future, but you need to accept what is right now in order to keep moving spiritually. The Spiritual Warrior accepts what is, then, in a state of freedom, chooses a reality and creates it consciously.