The red wisp was his soul energy. The size of it depended on his control of his soul energy not the quantity.
The red wisp showed that Sam's control of soul energy was at minimum. At this point, it was really useless to him.
As sir Humphrey had said, he would have to try and control his soul energy before he could help him.
Sam proceeded to try and move the red wisp with his mind, but it didn't respond. He tried a few more times, but his efforts looked futile.
'It's no use.' He said to himself. Sam was beginning to lose hope and confidence. He began to feel ignorant for listening to Fred's words instead of looking at the bigger picture.
Sam started losing focus. The red wisp of his soul energy became dimmer and less visible. Before he knew it, the wisp disappeared bringing his mind back to reality.
He opened his eyes with a solemn look on his face.
Fred in that moment knew something was wrong. "What? Did it work?"