We only fully grasp and tap into the infinite joy of the gospel after we understand, as Paul did, that we are the worst sinner we know (1 Cor 15;9-11; 1 Tim 1:15)
The person who knows he has received mercy while an undeserving enemy of God will have a heart of love for even (and especially!) the most ungrateful and difficult persons. Why? Because we are too.
If you truly care about the truth you will want people to believe it. Say it in the most hearable way possible without compromising in the slightest. Don't say it in an unnecessarily abrasive way and then, when rejected, pat yourself on the back for being valiant for truth.
It's true that God never misses a sin, nor does he ignore, nor does he minimize. But instead of responding with life-ending wrath against the transgressor, he looks down and sees the blood of his Son blotting out the sinful deed.
Sometimes the best wisdom is to not speak much at all. There are situations such that nearly any words will make conditions worse. When you meet with a grieving person who just lost a loved one, words should be sparing.
The main problem our heart has is not so much desires for bad things, but our over-desires for good things.
This is just a summary of St. Augustine: the primary sin is against the 1st commandment, to love anything (usually good things) more than God.
Dietrich Bonhoeffer was hanged by the Nazis on April 9, 1945 at the Flossenbürg concentration camp.
A camp doctor who was there gave this eyewitness account:
“On the morning of that day between five and six o’clock the prisoners, including Admiral Canaris, General Oster and state attorney Dr. Sack were taken from their cells and the verdicts of the court martial read out to them. Through the half-open door in one room of the huts, I saw Pastor Bonhoeffer, before taking off his prison garb, kneeling on the floor praying fervently to his God. I was most deeply moved by the way this lovable man prayed, so devout and so certain that God heard his prayer. At the place of execution, he again said a short prayer, and then climbed the steps to the gallows, brave and composed. His death ensued after a few seconds. In the almost fifty years that I worked as a doctor, I have hardly ever seen a man die so entirely submissive to the will of God.”
Bonhoeffer's last recorded words: "This is the end—for me the beginning of life."