Why did you decide to apply to this role?

Thank you very much, Sir.
I wish to, first of all, recognize and appreciate the good impact you are creating in this company. I am a web developer (or any role which you applied for!) by training and have always wanted to serve in a company where I will apply my expertise in my field, learn more, and grow. On seeing your offer, I realized it's the best opportunity for me to serve, learn and grow. Thanks

I decided to apply for this role because I think I can give something fruitful to you and your company as well I can also develop a great potential in myself.

To work or do something must be beneficial and keen to both as this makes the result more powerful and impressive. And I think this is the platform to show-cast myself with the best of me.