Now after they blew it let us see what happens

Bg 1.19

sa ghoo dhārtarāṣṭrāṇāṁ
h
dayāni vyadārayat
nabha
ś ca pthivīṁ caiva
tumulo ’bhyanun
ādayan

Word for word: 

sa — that; ghoa — vibration; dhārtarāṣṭrāṇām — of the sons of Dhtarāṣṭra; hdayāni — hearts; vyadārayat — shattered; nabha — the sky; ca — also; pthivīm — the surface of the earth; ca — also; eva — certainly; tumula — uproarious; abhyanunādayan — resounding.

Translation: 

The blowing of these different conchshells became uproarious. Vibrating both in the sky and on the earth, it shattered the hearts of the sons of Dhtarāṣṭra.

Earlier also it was described as tumula the sound was tumultuous, here also in 19.d the sound is described as tumulo ’bhyanunādayan and the timula has nabhaś ca pthivīṁ caiva it has extended all the way from the sky to the earth but the important point here is sa ghoo dhārtarāṣṭrāṇāṁ, this ghoa this proclamation this sound what is the effect of that on dhārtarāṣṭrā, the sons of Dhritarashtra? hdayāni vyadārayat, their hearts were shattered. Why was their hearts shattered? Because of the sheer volume of the conch shell and the confidence it conveyed it shook and shattered the confidence of the Kauravas so when the Lord and his devotees were blowing the conch shells this combination was undefeatable and the Kauravas realized that there are in deep trouble and after realization of this deep trouble their hearts were shattered. So these are all signs that the victory will be for Pandavas not to the Kauravas. Also BG illustrated that although everything is set for the victory at the least expected moment things can go wrong the Pandavas were prepared for battle and expected for win but let us see what happens now

BG1.19 Purport

…One who takes shelter of the Supreme Lord has nothing to fear, even in the midst of the greatest calamity…

How devotees are free from fear, actually courage is not necessarily the absence of fear it is the awareness of the presence of dwarf’s fear. If we have fear we just cannot switch them away, fear of future, fear of getting terrible disease, fear for misunderstandings. We can have different types of fear adhibhautika, adi-devika and adyatmika. Courage is not just absence of fear. Sometime People have no fear because of ignorance e.g. drunken person can run into a heavy traffic fearlessly that is not just fearlessness that is stupidity foolishness. So there can be fearlessness in ignorance, where one is so much lost in one thought and his own world that he is not aware of the dangers then there is fearfulness because one is so much dependent on the material world one wants to enjoy here and one feels fearful, how I will enjoy if this goes wrong or that goes wrong so much of anxiety comes because of that and beyond that is fearlessness which comes from knowledge when one understands that actually I am not the body I am the soul. Krishna is there and He will care for me, so fearlessness comes from the awareness of the presence of dwarf’s fear which means understand that God is there and in front of Him whatever fear is there that is insignificant by this courage comes knowledge of soul etc. that dwarfs (like a dwarf, very small) fear then courage comes. E.g. walking on a dark street one see a giant person coming one may be fearful whether he may rob me and at the same time one sees bigger police man with gun in hand then one will feel peaceful. So what has happened it is not that the robber is not there but I know someone bigger is there for me to protect. Similarly in our mind there are so many fears larking and those fears we can’t send them away but if they are there what we have to do is increase our Krishna Consciousness we have to be aware of the Presence of Krishna that dwarf’s fear then the fear goes away that is how we move forward in our spiritual life So Pandavas were not fearful since Krishna was with them but Kauravas were fearful because there were not aware of presence (of God / Krishna) that will dwarf their fear in fact that presence was on the opposite side as they have chosen the side opposite to the Supreme Lord and that's why their destruction was guaranteed.