That's a great teaching. I am going to share slightly different perspective regarding Tav.
At the end of any cycle of evolution, our Consciousness receives a ת Tav, a mark. When we complete the period of time we are allotted in a human organism, we receive a Tav. When we complete a Manvantara or a Mahamanvantara, we receive a Tav, a summation of our every action, our every movement. That summary is what propels us to the next stage. Humanity, in the many cycles through which it passes, receives mark after mark as we pass from age to age, from stage to stage.
In addition, every cosmic Initiation is a ת Tav. When our Innermost receives an initiation, it receives a Tav, a mark.
But the ultimate Tav, the final, greatest ת Tav, is written of in the Book of Revelation: it is that final ultimate synthesis of every movement of every action that we have ever performed in all of our existences. It is this Tav that we must be concerned about because it is this Tav that propels us to our ultimate destiny. ☺