I love how the AMP version puts this; Finally, all of you be like-minded [united in spirit], sympathetic, brotherly, kindhearted [courteous and compassionate toward each other as members of one household], and humble in spirit;

After a discourse on Unity between Husbands and wives, Peter follows with an exhortation for unity among all saints. While churches/denominations may have some doctrinal/theological differences as long as they we are pointing to the uncompromising Cross of Christ we should at least respect each other. 

With all the infighting and disrespect  It among “Christians”  it is no wonder the Samaritans (non believers) think we are not worth a second look.