Merciful in the Greek is; eleemon. It means to be compassionate. My prayer that while you witness to your Mormon friend you will have this type of mercy for them, they are in need of your compassion!
“Many have greatly misunderstood the place of mercy in the forgiveness program. Its role is not to give great blessings without effort. Were it not for the atonement of Christ, the shedding of his blood, the assumption by proxy of our sins, man could never be forgiven and cleansed…the Lord must now let justice rule, for he cannot save us in our sins.” Miracle of Forgiveness, pg. 358, Spencer W. Kimball