If Father is in one's heart, and one's heart is linked to all the other parts of one's body in some way, like via veins and arteries, then one shouldn't be harsh towards their parts of their body, as that would be to be harsh to the environment that Father resides within.  Much less, being harsh towards their own heart.  And if Father encompasses and resides within one's body, one's being, it should be understood that then what one is doing to theirself could be what they are doing to the One who resides in their being.

It was noted that before sin was introduced to paradise, that Father did not need to show Her strict and harsher side.  When Creation is back in full Unity with Father, ...

Where is the line drawn for when a person should continue to be strict and disciplined?

In this, I am reminded of...  Hmm...

If a person has already cultivated zeal and diligence, must they be further required to be strict and disciplined towards themselves?

A lesson given in 1 Kings 12:4 comes to mind.

Father answers and provides the means to find answers.  I believe it was told to us that the Word holds the answers to all our questions.