The commentary is over the part that says
Peace be upon you Ya Aba Abdillah, Peace be upon you O son of the Messenger of Allah, Peace be upon you O son of the Commander of the FAithful and the son of the leader of the inheritors (of the Prophet); Peace be upon you O son of Fatimah, the leader of the women of the entire Universe.
The true meaning of "As-Salam Alaikum" is not a mere "Hi", "Hello", "How are you" as we are accustomed to using today - it has a much deeper meaning than just a standard greeting. In actuality, there are three meanings for this greeting:
1. As-Salam, as we know, is one of the names of Allah. Thus, when we say "As-Salam Alaikum" we are actually saying that may the trait of Allah (as-Salam or peace and tranquility_ be upon you and may He protect you;
2. As-Salam is also in the meaning of submission or surrender. Thus, when we say "As-Salam Alaikum" we are actually saying that we submit to what you would like for us to do (obviously within the limits of the Shariah);
3. As-Salam is also in the meaning of protection or safety. Thus in this meaning, when we greet another believer with "As-Salam Alaikum" we are actually guaanteeing our believing brother or sister protection from any evil from ourselves and that we will not do a single thing to harm them - either physically or even spiritually. Not only would we not harm them with our hands, but we will also not cause them grief with our tongue...
Thus when we address Abi Abdillah and say "As-Salamu Alaika Yaa Aba Abdillah" we are saying that: 'May the peace and tranquility which Allah bestows upon His creations also be showered upon you. Truly, we submit to your mission and commandments and whatever you ask us to do. In addition, we shall not do a single thing to hurt you - either your physical presence or more importantly, your feelings.'
In actuality, we are promising the Imam that we shall not break the laws of Allah (since our Imam grieves when he sees us doing this) nor will we do anything to trample on the sacred goals and objectives which he laid down his life to protect.