And David said, “Is there still anyone left of the house of Saul, that I may show him kindness for Jonathan’s sake?” Now there was a servant of the house of Saul whose name was Ziba, and they called him to David. And the king said to him, “Are you Ziba?” And he said, “I am your servant.” And the king said, “Is there not still someone of the house of Saul, that I may show the kindness of God to him?” Ziba said to the king, “There is still a son of Jonathan; he is crippled in his feet.” The king said to him, “Where is he?” And Ziba said to the king, “He is in the house of Machir the son of Ammiel, at Lo-debar.” Then King David sent and brought him from the house of Machir the son of Ammiel, at Lo-debar. And Mephibosheth the son of Jonathan, son of Saul, came to David and fell on his face and paid homage. And David said, “Mephibosheth!” And he answered, “Behold, I am your servant.” 2 Samuel 9:1-6.
It was not usually the way of Kings to let another royal lineage live. But David did not kill or connive to get the throne. He waited for the proper time, when the throne would be vacated by another means.
Mephibosheth was likely aware of how Saul had declared his loyalty to David, only to try to kill him. It was the way of Kings, as far as he was concerned. So when David summoned him, he feared for his life.
Most people are like this with God. They think they know the ways of God; that He is cruel and vindictive. They hide from Him their whole lives, alien to the promises, believing they must be for someone else. To them, all calamity is caused by God, not by the curse brought on the world by man’s rebellion. What a difference it makes when you discover how much He has done, and wants to do, for you.