'We must sing'

We must sing songs that tell how to change things,'' soul singer Stevie Wonder told Harvard Law School students the other day. ''If it's law, use your experience for a better understanding of what is right; use your attention to change the law to make this a better place.''

Mr. Wonder shared insights into how he has joined the sheer joy and celebration of his music (''Isn't She Wonderful?'' ''You Are the Sunshine of My Life'') with public commitment, as in his support of issues like a federal holiday honoring Martin Luther King Jr.

''In my career I've learned that giving of your services freely gives you a good return on your investment, not just financially, but morally. It helps me measure myself, how I was and how I am.''

It's hard to imagine a training ground more suited to the hard contentiousness of modern life than the Cambridge, Mass., campus and a discipline more discriminating about interests than law.

But even non-Cantabrigians can appreciate Wonder's remarks: ''Without people, there'd be no laws, and without laws there'd be no lawyers. As a lawyer, you'll need to share your knowledge with those who never had the economic opportunity to even hire a lawyer. . . . You will need to give your services so that you can stay in touch with those who keep you going.''

Rounding out his message - closing the circle of fortunate and needy, entertainer and entertained - Wonder led his audience in singing ''Let Us Join Together As One and Have Some Fun.''