ashaastravihitam ghoram tapyante ye tapo janaah
    dambhaahamkaarasamyuktaah kaama raaga balaanvitaah  // 17.5 //

Those  men who practice terrific austerities not enjoined by the scriptures, given to  hypocrisy and egoism impelled by the force of lust and attachment,

karshayantah shareerastham bhootagraamamachetasah
    maam chaivaantahshareerastham  taanviddhyaasuranishchayaan// 17.6 //

Senseless,  torturing all the elements in the body and Me also, who dwell in the body, you  know these to be of demoniacal resolves.

The  wrong way of worshipping at an altar is described here. No spiritual  enlightenment can be expected in wasting one's energy in wrong channels in the  name of religion. Sri Krishna says that physical persecution of one's own body  and self-denial would not constitute an austerity following which one would  expect spiritual unfoldment and inner personality development. Some people  undertake severe austerities merely as a show out of egoism and hypocrisy with  a view to satisfy their lustful desires and attachment to worldly objects.

Even  if such people gain anything out of such austerities they will only misuse  their new found strength for wrongful purposes and ultimately destroy  themselves. These people belong to Asuric type. Such unintelligent practices  oppress the bodily elements and also the Self or the Divine Lord within.  Intelligent control is Tapas but not cruel self-torture.

THREE KINDS OF FOOD

aahaarastwapi sarvasya trividho bhavati priyah
    yajnastapastathaa daanam teshaam bhedamimam shrinu  // 17.7 //

The  food also which is dear to each is threefold, as also sacrifice, austerity and  alms giving. You hear the distinction of these.

The  temperamental influences which govern the mind, thought and actions of a man  are enumerated here. The Lord analyses one's inward nature and consequent outward  expressions when one is under the influence of any one particular Guna.

The  choice of food, friends, and types of emotions entertained and the view of life  in general are all indicative of the type to which the seeker belongs. In the  choice of one's food, in the type of sacrifices one will make, in the kind of  Tapas one will indulge and in the quality of charity one will make, any one of  the three types of faith can be discernible.

aayuh sattvabalaarogya sukha preeti vivardhanaah
    rasyaah snigdhaah sthiraa hridyaa aahaarah  saatwikapriyaah // 17.8 //

The  foods which promote life, purity, strength, health, joy and cheerfulness, which  are sweet, soft, nourishing and agreeable are dear to the Sattvic people.
  Sattvic  persons like the food which increases vitality, supplies energy, enhances  strength to resist temptations from the sense objects, provides health, augments  joy and inward cheerfulness.

katvamla lavanaatyushna teekshna rooksha vidaahinah
    aahaaraah raajasasyeshtaa duhkhashokaamayapradaah  // 17.9 //

The  foods that are bitter, sour, saltish, excessively hot, dry, pungent and burning  producing pain, grief and disease are liked by the Rajasic.

Rajasic  men to fulfill their uncontrolled passions desire food that has strong  qualities like bitterness, sourness, hot, pungent etc. Although such food  produces good amount of energy ultimately it leads to a life full of pain,  grief and disease.

yaatayaamam gatarasam pooti paryushitam cha yat
    ucchishtamapi chaamedhyam bhojanam taamasapriyam //  17.10 //

That  which is stale, tasteless, putrid, rotten, refuse and impure is the food liked  by the Tamasic.

The  kind of diet we take has its influence on our power of self control.

THREE KINDS OF SACRIFICE

aphalaakaangkhibhir yajno vidhidrishto ya ijyate
    yashtavyameveti manah samaadhaaya sa saatwikah // 17.11  //

That  sacrifice which is offered by men without desire for reward, as enjoined by the  ordinance (scriptures), with a firm faith that sacrifice is a duty, is Sattvic  or pure.

“The  Yajna of the Gita is not the same as the ceremonial sacrifice of the Vedas. It  is sacrificial action without expectation of any reward by which man dedicates  his wealth and deeds to the service of the One Life in all. People with such a  sacrificial spirit will accept even death gladly, though unjustly meted out to  them so that the world may grow through their sacrifice. Good people maintain  the world through their suffering and sacrifice”. Dr.S.Radhakrishnan.

abhisandhaaya  tu phalam dambhaarthamapi chaiva yat
    ijyate  bharatashreshtha tam yajnam viddhi raajasam // 17.12 //

The  sacrifice which is offered, O Arjuna, seeking a reward and for ostentation, you  know that to be a Rajasic Yajna.

In  order to get some chosen result some people perform actions, while some others  do so merely for show and to satisfy their vanity. These acts do not constitute  Divine act nor can they bring about inward cheer or peace. Such sacrifices are  termed Rajasika.

vidhiheenam asrishtaannam mantraheenam adakshinam
    shraddhaaavirahitam yajnam taamasam parichakshate  // 17.13 //

They  declare that sacrifice to be Tamasic, which is contrary to the ordinances of  the scriptures, in which no food is  distributed, which is devoid of Mantras and gifts and which is devoid of faith.

Disregarding  all the requirements laid down in the scriptures, acting against all Vedic  injunctions i.e. acts which are against all the principles of right living  belong to the lowest type. These actions in which food is not distributed i.e.  where no sharing of wealth with others takes place, where rituals are conducted  without Mantras and without Dakshina or distribution of reward are all Tamasika.

The  distribution of food and the payment of the fee are symbolic of help to others  without which all work is self-centered.