Which lines in this excerpt from act iii of shakespeare’s macbeth refer to macbeth’s insecurity because of the threats to his kingship?

These are the lines from Macbeth's soliloquy,
"Upon my head they placed a fruitless crownAnd put a barren scepter in my grip,Thence to be wrenched with an unlineal hand,No son of mine succeeding. "

His kingship is in the threat of Banquo since he doesn't have a son to pass on his throne while Banquo has.