"The entire matter that I command you, you shall guard it to do; you shall not
add to it and you shall not subtract from it."
Here we are told according to the Chachomim - althought the verse may make it obvious - that we are forbidden to add mitzvos to either the Oral or Written Laws. According to various commentators, this commandment forbids adding prohibitions to the already existing prohibitions of the Torah.
The importance of this mitzvah in relation to the Torah and all its commandments is in understanding that these mitzvos were given to us by a perfect G-d and that any deviation in observance is an affront to Hashem and to His purpose
Wouldn't Hashem want us to do extra things to increase our connection with Him or wouldnt He want us to make things easier for us to become cloeser to Him by maybe taking the more difficult Mitzvos away??
I would like to Pose two answers to this question!
1. There is nothing extra a person could do in this world than keep the 613 Mitzvos! The mitzvos are all encompassing any situation we could ever be in, there should be no reason to add to the Torah!!
2. So supposing there is a reason we should and therefore could add to the Torah whats the problem with adding to it?? A parable serves to elucidate this point. If a master had ordered his servant to remove some dirt from a garment, and the servant went out of his way to wash, dry and press the garment, the master would most certainly have been pleased with the servant's hard work and devotion on his behalf in doing more than had been required of him. However, if a doctor prescribed a certain medication for a patient who was ill, and that patient did not take the required dosage but doubled it, the doctor would definitely have been angry with the actions of his patient.
The difference in the reactions of the master and the doctor centers on the following consideration. While both the servant and the patient disobeyed orders, in the first instance the orders were given for the benefit of the
master and, therefore, the more work the servant did the happier his master was. In the case of the doctor and patient, the orders were given for the patient's benefit and were to have been obeyed to the letter so that the medication would serve its purpose.
Our relationship to G-d is analogous to that of the patient and doctor. The mitzvos are medicine for the soul. It is, therefore, forbidden to deviate even slightly from the prescribed manner of observing them.