These verses are important in many ways as they bring out the essense of tattvavada.
First it portrays God as the destroyer , a concept unique to the BG.All religions see him as compassionate kind and tender .But only the BG has the boldness to put forward the idea of god as the destroyer , hold reality in the face of man , and tell him , "This is also god" and you know him as this also.Not only as the lovable krishna who steals butter , but also as one who makes a meal of this world.
Thus it offers us a holistic view of life and shakes off any sentimental feelings of non-violence and pacifism that we may harbur and asks us to stare at reality in all its embodiment.
Thus we must embrace life as it is , ready to admire the innocence of the child but also willing to take the sword and slay the "anaryas" the ignoble peoples.For that is also gods work and god created the world in that way so he can bring out those aspects of life in also.It is also a duty we must perform , not shrink away from reality but accept reality as it is.
Secondly the verse also establishes the superiority of Vishnu.Krishna says , "Even without you they will be destroyed by Me".The import is everything is a part of My plan and My plan triumphs and not yours.One cannot alter the lords plans in anyway.
Arjuna had a limited moralistic vision of the buddhist type , concerned about physical violence in the material plane.He was kind of moralistic which is a materialistic philosophy.These verses and the Vishwa Roopa darshana remind Arjuna of the existence of the Supreme Lord as a reality and as a higher principle acting on this world and deciding on its fate and how he must submit to Its workings , casting aside all partial dharmas(sarvadharmas) and surrended on to me(mam ekam saranam vraja)
Arjuna also had a false ego , thinking himself to the doer , and taking responsibility for the fate of mankind and society.He was afraid that if this war was fought , there would be large scale destruction , may be even the bharata race would come to an end.He was worried about the destruction of varna system , the corruption of women and the end of morality.
In other words he was socialistic , worried about society and its fate , like our modern day communists and humanitarians.
Krisna reminds him that all is His working , by His Will , the armies have been drawn against each other , and by his will the entire Bharata race will be destroyed for the sake of a new begining.And that he must simply carry out the Lords plan and not consider himself with socialistic ideas as the final philosohy.For out of this apparent destruction will come a greater good.
Arjuna is reminded all servants of the Lord.
In the subsequent verses the Lord says that "Fight and win a prosperous kingdom" and he has to be the instrument of the Lord in ensuring the victory of the divine forces , that is consider himself as Lords servant and do His bidding and not ponder over limited ideas.