Mindfulness and being aware of our reactions in meditation helps us to understand the causal relationship of things. This is the practice of watching the hindrances, we get to see how when we have a thought in the mind what type of reaction comes in the body. So as we use mindfulness, and just note the hindrances when they arise, we are also doing what we call investigation. Investigation into cause and effect. For example, when aversion is present we note "aversion, aversion". We then try to bring our attention to the body and see the resulting reaction in the body. If we practice, we start to see that aversion brings tightening. Tightening in the stomach, in the shoulders, etc. Sometimes we find the hands are clenched, the eyes are closed tight. We see that our reactions of anger bring the result of stress in the body. The same with fear, worry, etc., we start to note them. This is the importance of developing mindfulness of the thoughts, because then we can see and understand for ourselves this law of cause and effect. This is looking at the law of Kamma moment for moment.
We also realize that when we develop the opposite wholesome thoughts, like Compassion and Lovingkindness, the resulting reaction in the body is the fading away of this tightness. We see this natural law of cause and effect. So as we develop meditation we actually s see, yes, it reduces stress. Wise meditation reduces stress.
Now we can learn to use the stress that is arising in our meditation to our benefit. Say when a hindrance such as aversion arises we note it, "aversion, aversion". We examine it in the body using the investigative quality in the mind, which helps us to develop wisdom about cause and effect. As we investigate into this, if we actually understand this stress, that this Dukkha we are experiencing arises because of this thought in the mind, this brings up the Compassionate Understanding that enables us to have Compassion for ourselves. We're then investigating into the Four Noble Truths.
Dukkha, what is the cause of it? It's ignorance. What is the ending of it? Developing the Compassionate Understanding we let go. Then we see the fading away of the stress. So as we develop meditation we start to understand, yes, we don't need all these fancy gadgets to tell us that meditation helps us to reduce stress.