How do I explain to a Lutheran the Catholic focus on the Passion and the crucifix?
The short answer
Jesus redeemed us on the cross on Good Friday, not on Easter Sunday, and he said his disciples must take up their cross and follow him. To look at the crucifix is to recognize the greatest event in history and the infinite love we are blessed to know by faith.
Jesus did not redeem us on Easter Sunday; he redeemed us on the cross on Good Friday. He also said that to be his disciples we must deny ourselves, take up our cross and follow him (Matthew 16:24-27). Nowhere in Scripture does he replace that focus with Easter Sunday.
To look at Jesus hanging on the cross is to recognize the greatest event in history. It reminds us how unable we are to grasp fully his infinite love, and how infinitely fortunate we are to know that love, however imperfectly, through the gift of faith.