“Parvaan Karo” does not make any sense not because it is irrational to pray for Degh parvaan to Guru Sahib. What makes anyone think Degh prepared according to maryada by a rehatvaan Sikh would not be parvaan? Preparation of Degh according to maryada is by default parvaan. Traditional words of “Bhog Laavo” are proper and according to Gurmat. Missionaries have unnecessarily started saying parvaan because Brahmins say bhog to their deities but they do not realize that idols are not divine and Guru Sahib is alive, Divine and has consciousness. Few points to consider against "parvaan" wording:
1) Why isn’t degh prepared according to maryada by a rehatvaan Sikh parvaan?
2) At what point is it considered parvaan?
a) If from Hukamnama, then is Hukamnama taken solely for this purpose? If no then shouldn’t separate hukamnama be taken? What if degh is parvaan but not langar so what kind of hukamnama can we expect? Should two separate hukamnamas be taken for langar and degh? Further, has there been any instance where degh was not parvaan and it was thrown away and prepared again? Can any advocate of “parvaan” answer this? If hukamnama gives indication of parvaan then why is kirpan bhet done? Hukamnama renders kirpan bhet a useless practice.
b) If kirpan bhet is a sign of parvaan then there is no need to either pray for it or take hukamnama
On the other hand, wording bhog does not raise any issues. Bhog does not simply mean to eat but has many meanings. Bhog generally refers to food presented to deity. So in this context, bhog means food presented to Satguru for his blessings. In Gurmat, the only deity worthy of worship is Vaheguru who sis present in Gurbani. So we present food to Guru Sahib. According to maryada, degh must be brought in during diwaan while kirtan is being recited. So kirtan instills Bhagti aspect and kirpan bhet instill Shakti aspect in the degh (and langar). It is a combination of miri and piri, bhagti and Shakti. We pray for bhog because we are requesting Guru Sahib to exercise his kala to bless the degh with bhagti and Shakti so whoever eats it gets nihaal with these two qualities.
Consider Amrit Sanchaar example during which no one prays for Amrit parvaan because as long as maryada is followed, it is Amrit. But Ardaas is done to Guru Ji to bless the Amrit with His power. Gurbani and khanda combined instill saint-soldier qualities. Degh and langar are no different.
I do not in any way mean that Guru Sahib cannot eat degh. Guru Sahib’s body is not like ours so His eating would be as it behooves His Shabad Moorat. What I mean to stress it that bhog doesn’t just mean to eat. Degh is not a “seet parshaad” because no food eaten by Guru Sahib can ever be jootha. Guru Rakha