To awnser you properly , when it says that God will seek vengeamce , he is speaking to his people and followers , so christians. What he means that you as a believer should not seek vengeance for adversity is a human trait , where as peace is a fruit of the spirit . So this is speaking on how we should treat one another. Now when he means vengeance he means those who would persecute you because of God and as God has the right to cast judgement on all those who seek to hurt or threaten his children. That's not to say god doesnt love non-believers (God loved us all first) he wants to protect his children and punish those who do wrong to them Its not our jobs as human being to seek vengeance for our own sake but love one another and show patience because he shows us patience