BG Chap 14 - The modes compete for supremacy
The modes are not constant in their influence on the living entity. According to our karma, our work, our association, our choice of food and so on, a particular mode becomes predominant within us. The nature of the guṇas is that they appear and disappear according to operation or exhaustion of old karmas. Sattva becomes prominent with the disappearance of rajas and tamas. It appears because the other two modes become invisible. Rajas becomes prominent with the disappearance of sattva and tamas. Tamas appears from the eclipse of sattva and rajas. When one mode becomes strong and the others are weak, it produces its particular effects previously described. Although there are these three modes of material nature, if one is determined he can be blessed by the mode of goodness, and by transcending the mode of goodness he can be situated in pure goodness, which is called the vasudeva state, a state in which one can understand the science of God.