Speaking the truth in love means:
The truth needs to be spoken, the clear, unvarnished truth of scripture. It represents things as they are.
The truth spoken in the original language means “truthing in love” it is seen as walking or holding up the plain truth of scripture in Calvary love or agapao love (3 John 4).
The truth must be spoken without a sour, unfeeling disposition and a genuine concern and love for others spiritual welfare.
The truth has a goal of maturity of the hearer which has for its model Jesus Christ who is the truth (John 14:6).
The truth is necessary because we are members of one body and when one part is infected all are in danger of being hurt (Eph. 4:25).