The Christian Perspective

If morality is obeying god, then obeying god is morality.

If we grant the former, then the latter follows by tautological necessity.

Is it circular?

Insofar as tautologies are circular, sure. Here is another circular tautology:

If 2 + 2 = 4, then 4 = 2 + 2.

Totally circular.

Malachi 3:18; Romans 4:15, 5:13; 1 John 3:4.