Here's good quote I read about the same time Lesson 28a became available. I think it speaks well to the question of tithing we were "talking about" awhile back. I thought I'd pass it on.

"To receive more we must give out what we have received. If we withhold what we receive, stagnation will follow and we will be like the wheel that generates power from the water and suddenly, of its own volition, begins to withhold the water which it is using. It will soon find itself stifled with inert water. It is only when the water is allowed to flow freely through that it is of value to the wheel to create power. Just so with man. When he contacts God's ideas he must give them out in order to receive the benefit from them. He must allow all to do the same, that they may grow and develop as he is growing." (Volume 1, Life & Teaching of the Masters of the Far East, Baird T Spalding)

I think it's saying that we must allow the ideas we are learning here to flow through us. That can be "not hiding your light under a bushel", as well as giving away money. Allowing (giving) your new found self to shine through can be just as beneficial to others. (That is why some of us are finding old friends drift away, they don't want to see that light just yet.) Being in the Certain Way all the time is enough. We don't have to do anything else for the good to come to us and to pass through us to everyone else. That, to me, is tithing, living what we have learned here, walking the walk. Money is just a part of the energy that flows through us.