seize the moral high ground
To claim, purport, or make it appear that one's arguments, beliefs, ideas, etc., are morally superior to those espoused by others. The senator always tries to seize the moral high ground during a debate so as to shift public opinion in his favor.
seize the moment
To take full advantage of life's opportunities whenever and wherever they present themselves; to live life to one's full potential. I've tried to get the most out of life by always seizing the moment. That's how I ended up living in Europe and fell in love with your father!