Look at the meaning and use of indiferente in the DLE:

indiferente 3. adj. Que no despierta interés o afecto. Ese hombre me es indiferente.

As you see, in present "ser indiferente" (not to arouse interest or affection) is commonly used with the structure me/te/le/les/nos... + es + indiferente.

Ese hombre me es indiferente -> I am indifferent to that man

 

La guerra me es indiferente -> I am indifferent to the war

So with "Que la guerra no me sea indiferente", the author expresses that he does not want to be indifferent to the war.

Look at the meaning and use of indiferente in the DLE:

indiferente 3. adj. Que no despierta interés o afecto. Ese hombre me es indiferente.

As you see, in present "ser indiferente" (not to arouse interest or affection) is commonly used with the structure me/te/le/les/nos... + es + indiferente.

Ese hombre me es indiferente -> I am indifferent to that man

La guerra me es indiferente -> I am indifferent to the war

So with "Que la guerra no me sea indiferente", the author expresses that he does not want to be indifferent to the war.

Look at the meaning and use of indiferente in the DLE:

indiferente 3. adj. Que no despierta interés o afecto. Ese hombre me es indiferente.

As you see, in present "ser indeferente" (not to arouse interest or affection) is commonly used with the structure me/te/le/les/nos... + es + indiferente.

Ese hombre me es indiferente -> I am indifferent to that man

La guerra me es indiferente -> I am indifferent to the war

So with "Que la guerra no me sea indiferente", the author expresses that he does not want to be indifferent to the war.

Look at the meaning and use of indiferente in the DLE:

indiferente 3. adj. Que no despierta interés o afecto. Ese hombre me es indiferente.

As you see, in present "ser indiferente" (not to arouse interest or affection) is commonly used with the structure me/te/le/les/nos... + es + indiferente.

Ese hombre me es indiferente -> I am indifferent to that man

La guerra me es indiferente -> I am indifferent to the war

So with "Que la guerra no me sea indiferente", the author expresses that he does not want to be indifferent to the war.