'Able' in the Bible

The men of Beth-shemesh said, “Who is able to stand before the Lord, this holy God? And to whom shall He go up from us?”

If he is able to fight with me and kill me, then we will become your servants; but if I prevail against him and kill him, then you shall become our servants and serve us.”

Then Saul said to David, “You are not able to go against this Philistine to fight with him; for you are but a youth while he has been a warrior from his youth.”