Gratitude and appreciation helps bring the mind back to the present and away from thoughts of the past or future. 

Sometimes our thoughts of the past can be painful or make us feel negative feelings. Similarly, thoughts of the future can make us anxious or worry causing us to worry about things that haven't happened or we think might happen. These thoughts bring us down or lower our mood, 

If we are grateful and appreciate we focus on now, the present. We bring our awareness and attention back to positives and away from those negatives of the past and future.