Probe
Harry kept his focus on the small white flame inside of him, he had already activated 'energy control' and his proficiency in channeling his energy had improved so it was now a lot easier for him to control his energy.
In order to channel mana outside of the body, one had to first coat the inner layer of the body with a thin line of mana.
It didn't have to be moderately circulated around all parts of the body but only where the mana was going to be channeled from.
This process was easier for elementalists as they used elemental mana rather than raw mana, they would face less resistance.
The main aim of this was to reduce the resistance and let the mana come out of the body easily.
The human body had a natural resistance against mana, it was like drawing out water from a bottle without opening the bottle or making a crack in the bottle.
However, in Harry's case, he had to channel his energy into the crystal.