- Shiva - the name is very powerful and means auspiciousness
- Shiva + Shakti - Shambhava and the name Shambhu is derived from this - which means the one who is always embedded with limitless power
So, invoking these names will connect to the deity - if one does it with enough intensity and devotion. Names are very powerful - especially specific names such as these. While a mantra requires technical knowledge: initiation, specific details of visualization, how to align it with the breath, how to recite it in different chakras, how to place the syllables of the mantra in one’s physical and astral body, how to apply the mantra to attain different results, etc.
All these technicalities are recorded and taught for a “mantra”. For chants such as reciting the names, none of these apply - it is just devotion and concentration; Mantra is a whole different game. Intensity does not mean volume. It means how strong one’s determination to invoke the deity is, how mindful one is, etc. The least beneficial recitation is verbal and loud, the most effective is the silent mode of recitation (for mantras).
I write this because not everything is a mantra. A mantra is one which is (a) revealed by a realized sage (b) Has been practiced by a lineage of realized teachers (c) The details and applications of the mantras are recorded based on millenia of use.