Speaking to his followers, Jesus said:
“A new command I give you: Love one another. As I have loved you, so you must love one another. By this all men will know that you are my disciples, if you love one another.” (John 13:34-35, 1984 NIV)
Writing to Timothy, Paul wrote:
And the Lord’s servant must not quarrel; instead, he must be kind to everyone, able to teach, not resentful. Those who oppose him he must gently instruct, in the hope that God will grant them repentance leading them to a knowledge of the truth, and that they will come to their senses and escape from the trap of the devil, who has taken them captive to do his will. (2 Timothy 2:24-26, 1984 NIV)
You cannot say anything on your own that will change someone. It is through the Truth that God will work in their hearts. Deliver the Truth lovingly with sacrificial living to back it up.