rajas tamas cabhibhuya
sattvam bhavati bharata
rajah sattvam tamas caiva
tamah sattvam rajas tatha

"Sometimes the mode of goodness becomes prominent, defeating the modes of passion and ignorance, O son of Bharata. Sometimes the mode of passion defeats goodness and ignorance, and at other times ignorance defeats goodness and passion. In this way there is always competition for supremacy."

The Lord manipulates three words in a beautiful cycle! When stvam, rajas and tamasare inherent, how each one induces the other? One causes happiness, another causes activities and yet another, carelessness. How each separately works? We also do not see that one individual is always in happiness, another person in activities alone or a third person is always careless. Each of us is, in our lives for some time careless, for some time very active and for sometime happy. Within us, we see all these changes. So, how do these three induce us in a particular effect? Why they are not equal? Bharata = Arjuna! [hinting that Arjuna true to his Bharata dynasty, should exhibit sattva quality alone]. The mother of Swami Tiruvaimozhi Pillai, of this place, was called Satvikai Ammal [சாத்விகை அம்மாள்]. Abhibhuya = suppressing, rajas tamas = rajo and tamo qualities, sattvam = sattva quality, bhavati = remains [prominent]. Sometimes, sattva guna will surface, pressing below rajo and tamo qualities. [Similarly] rajah = rajo quality [will supress], satvam tamas = sattva and tamo qualities, tamoh = tamo quality [will supress], sattvam rajas = sattva and rajo qualities. Thus at any instant sattvam or rajas or tamas will dominate and keep the other two qualities suppressed. Whichever quality is predominant, that would cause its effects. This is the reason why we behave in a particular way at a given time, Sri Krishna tells. This is the reason why we are happy at some time, do wrongly by carelessness at some other times and be active at other times. Why this happens so? is very important. Over our many births we have accumulated Punya and Papa. Due to Punya karma, we get the blessings of the Lord. Those blessings will induce sattva quality to be prominent. This is one equation. Our accumulated papa, cause the dislike of the Lord, Who wants to punish us. This causes rajo or tamo qualities to be prominent. In addition to this, food habits have an effect on the prominence of sattva or rajas or tamas qualities. This is another part of the equation. Therefore, with Punya and consequent blessings of the Lord, plus the sattvika quality food, will enhance sattva quality. Similarly, with accumulated Papa, and consequent anger of the Lord, plus food that stimulates rajo and tamo qualities, will enhance rajo or tamo qualities in us. Therefore, what we have to do is to do atonement for our Papa, and get rid off ill effects, worship the Lord to have His grace and blessings and control our food habits to yield sattva quality. In our body, according to Ayurveda, vada [gas], pittha [bile] and kabam [phlegm] are to be equally balanced. Food habits can stimulate either vada or pittha or kabam to increase, causing disease. We are to expel stool, urine and sweat. If these are not expelled properly, then we get an illness. Similarly, in sattva, rajas and tamas, anyone dominates and cause effects. So we are clear that we have to do Punya karma, have proper food and seek the blessings of the Lord. This will stimulate sattva quality in us. 
                                                                                 (continued)