"Why Wear A Rudraksha?" = from Sadhguru answers

Every substance in the universe has a certain reverberation to it. We try to identify things that will support us in a particular direction. Not only rudraksha – all kinds of plants, flowers, animals – everything has been identified as to what will take us in a spiritual direction and what will not. 

 Rudraksha has this quality too –

   in a way, it becomes a part of your body. If you have worn it for one or two years, 24 hours a day, and one day, you take it off and try to sleep, you will not be able to sleep. It will feel as if a part of your body is missing, because the rudraksha has become a part of you and it functions like that – as an extra organ. The main purpose of this organ is to make you available to Grace. Because no matter what yogic practices or whatever else you do, ultimately, you become a possibility only by becoming available to Grace. This is why devotees attain quicker than anyone else, because they offer themselves. If that sense of offering is not brought in, yoga will be nothing but a circus.

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Full article.

Another thing about rudraksha is that it creates health. For all those who are only interested in living more donkey’s years, this is the most important aspect. They are not really interested in how they live – they just want to live longer. For what? If you check their “happiness-meter” from morning to evening, it does not touch any heights. ​Whatever you do, there will be no success in any area of life – whether it is the spiritual process, health, wealth, or anything else – if you do not become available to Grace. Either you have to become consciously available to it or unconsciously, in your own way. Without some amount of Grace, no human being, no creature would be alive. But if you consciously make Grace a part of your life, everything will work easily and smoothly. It will be a well-lubricated life. Rudraksha enhances that possibility. We want to use every support that is available to us.