Programming :: Pthread_cond_wait - When Thread1 Invokes The Mutex Lock - No Other Threads Can Access It In Parallel

If multiple threads operate on a single shared resource, we can lock it using pthread_mutex_lock. Uptill that it is fine, but why again pthread_cond_wait?

int shared=0; // global
.
.
// Thread 1
pthread_mutex_lock(&mutex);
shared=1;
pthread_mutex_unlock(&mutex);

When thread1 invokes the mutex lock, no other threads can access it in parallel. So why again and what for we use, pthread_cond_wait( ).