When Christ had his forty day of fasting, he didn't keep doing things as usual. He went out to the desert to be with God. Today Isaiah is warning against doing the same old thing and calling it Lent.
One more thing: What am I fasting from during Lent? Christ makes it clear that simply obeying the law is not the empty action He is looking for. Today is a day of fasting. Take a look at the list in the first reading and decide together as a family what you will fast from: fighting, selfishness, disobedience. Make it truly a different kind of day!
Prayer: Lord Jesus, I pray that people will know me as a Catholic Christian by the love they see in my actions, not simply the rules I follow. St. Mansuetus, pray for me. Amen.