'Be on Your Guard' in the Bible

Be on your guard against your fellow men, for they will betray you to courts of law, and scourge you in their Synagogues;

Presently Jesus said to them: "Take care and be on your guard against the leaven of the Pharisees and Sadducees."

How is it that you do not see that I was not speaking about bread? Be on your guard against the leaven of the Pharisees and Sadducees."