Tithing is a voluntary contribution. It is a giving back where you got your spiritual nourishment, your inspiration. It is keeping the blessing in movement. It is an expression of your abundance regardless of the circumstance, so it is also a state of mind creator. It has its roots in the Jewish mitzva (commandment) of leaving the edges of a cultivated land unharvested so the poor can come and collect the food. The Jewish long sideburn is a reminder of the mitzva, and tithing has some relationship to it with the Christian twist of where to give back.
I have found that tithing is a great activator of the Law of Attraction. Especially if you give often, and with the right mindset. According to Kabbalah the right mindset is a kind of spiritual or enlightened greed, give hungry for your own growth and your own enlightenment, and not from do-gooding. do-gooding is from ego (Satan)
My specialty is the mindset (or the seed level) of spiritual growth.