A 'mote' is a tiny speck of dust; a 'beam' is a large wooden plank. Jesus uses vivid humor to show how ridiculous it is to focus on others' small faults while ignoring our own large ones.
Memory phrase: The plank in your own eye
Talk about it: Can you see the funny picture Jesus is describing — someone walking around with a huge plank in their eye?
Prayer: God, before I look at other people's faults, help me look at my own heart first. Keep me humble.