What is meant by the word "Al-Wahdaniyah" (Oneness) that Abu Yazid al-Bistami mentioned in his saying, "the emptiness of the heart for Al-Wahdaniyah," when he was asked about Allah's Greatest Name?

Perhaps he meant that if a servant empties his heart for Allah alone, intending Him and none other, and attaches himself to Him, his supplication will be answered by any of His Beautiful Names. Thus, he will gain from it the same benefit as from the Greatest Name of Allah. This means that the Greatest Name is attained through a state of faith, not merely by utterance. It is every Name of Allah by which a servant calls upon his Lord, being completely absorbed, such that at that moment there is none in his thoughts but Allah.