Bg 3.28

tattva-vit tu mahā-bāho
gu
a-karma-vibhāgayo
gu
ṇā gueu vartanta
iti matv
ā na sajjate

Word for word: 

tattva-vit — the knower of the Absolute Truth; tu — but; mahā-bāho — O mighty-armed one; gua-karma — of works under material inuence; vibhāgayo — differences; guṇāḥ — senses; gueu — in sense gratication; vartante — are being engaged; iti — thus; matvā — thinking; na — never; sajjate — becomes attached.

Translation: 

One who is in knowledge of the Absolute Truth, O mighty-armed, does not engage himself in the senses and sense gratication, knowing well the differences between work in devotion and work for fruitive results.

tattva-vit, one who is a knower, Krishna has used Tattva Darshina is 2.16, Tattva Darshina means seer of truth Tattva-vit means knower of truth.

gua-karma-vibhāgayo,

guṇā gueu vartanta, the modes are acting in relation with each other

iti matvā na sajjate, knowing this a person doesn’t become attached

So Krishna is saying tattva-vit, the person who is knower of the Absolute Truth such a person understand when I am acting as a Brahmana when I am studying Shashtra or teaching Shashtra, I might become proud I have so much knowledge, I know far more than other people and see how nicely I give classes so if I act like this then I am misidentifying with my psycho physical nature and that sort of mentality will cause me bondage. But if I understand guṇā gueu vartanta that means the senses and modes are interacting with each-other and basically in material field the action is performed according to my nature. Then I will not become bound because I understand that this is my nature this is how I will be acting guṇā gueu vartanta so in this way we will be able to act and move forward in our life, if we take things systametically guṇā gueu vartanta, so I do guṇā gueu vartanta Krishna is telling over here because modes are acting so neither you surrender to the modes not you completely try to resist the modes neither are possible so

tattva-vit knows that if I will not be attached I will not be bound. iti matvā na sajjate, na sajjate means that the person says that I will not become bound by this.

So all these may seem abstract and philosophical for us because to familarize ourselves to the concept of three modes only will take sometime, but essentially what this means is that When a conditioned soul becomes Sadhaka he understands that I am trapped in a machine (this body) and as a machine it has certain pushing and pulling by default, like in computer certain setting are default and it will be active as soon as the machine is on.

Based on our past life our body and mind has certain tendencies although it can be changed, but changing of default setting, it doesn’t happens automatically, it requires certain continuous involvement and effort. Similarly the body has certain default setting when soul acts, although soul is transcendental but when the soul is within body and is acting in material realm the soul will act according to the default setting of the body, the soul moves step by step toward spirituality which means by acting as per default setting but keeping within the limit of dharma.

So I have a nature of a Sudra and I am thinking that I wanted to act like Brahmana. There is no problem a Sudhra can also become devotee of Lord, they can practice their own dharma and become elevated.

So here Krishna is saying recognize that the modes are the doers and don’t let modes take you on ride which is outside Dharma and at the same time don’t completely resist the modes also neither is possible, regulate it,

Here BG offers middle way, iti matvā na sajjate

SP Purport: According to Śrīmad-Bhāgavatam, one who knows the Absolute Truth in three different features – namely Brahman, Paramātmā and the Supreme Personality of Godhead – is called tattva-vit, for he knows also his own factual position in relationship with the Supreme.