Paul is exhorting believers in unity and love.  In Eph. 4:11-14, he says that God has ordained pastors and teachers for the edification of His people, that they might come to this unity and abound in Godly love.  Pastors and teachers are to encourage God's people in the faith.  They are not sent to rule as tyrants.  They are not sent to ridicule and embarrass.  They are not sent to be moral watch-dogs over people.  They are sent to preach and teach God's Gospel, its particulars and implications, all aimed towards the glory of God in Christ, the salvation of sinners, and the edification and growth of God's people.
 

How can pastors and teachers attain this goal?  They attain it by "speaking the truth in love."  The greatest love we can show anyone is to tell them the truth in light of God's Gospel of eternal salvation and final glory based on the righteousness of Christ alone.  The greatest love we can show to lost people is to tell them the truth of how they are lost and how their deeds are evil in light of the only way of salvation revealed in the Gospel.  The greatest show of compassion is to expose their disease (the guilt and defilement of sin), and then show them the only remedy (Christ established a righteousness that demands the salvation and final glory of all for whom He lived, died, and arose).  The greatest show of love we can give to saved sinners is to comfort them with the assurances of grace and salvation based on God's testimony.
 

Truth and love go together.  The lost world will not recognize this love as they do not know us (1 John 3:1).  Some have said that people will not listen to your doctrine until they see your love.  Now we desire that people know that we love them, but such a statement is not true of God's people as they recognize the love in telling them the truth, and it is not true of lost people as they view the truth of the Gospel as unkind and mean because it exposes that they are lost and that their deeds are evil (John 3:19-20; 7:7; 16:1-3).  One thing we know – there is no love in promoting any person in a false refuge by speaking peace to them when there is no peace based on God's Word.  That is only self-love.