The Prophet was 'Mawla' (Leader) and Imam Ali (A.S) is also 'Mawla' and the Prophet reminded people of this truth on Al-Ghadir Day. He publicly announced this fact so that everybody knew although Imam Ali (A.S) was not a prophet; he had the authority and leadership over believers as Prophet's successor.
Many Shias use the Hadith of Al-Ghadir in order to prove the truth of Caliphate of Imam Ali (A.S) and his succession to the Holy Prophet of Allah. However, the last sermon of Prophet Muhammad (PBUH) is so profound and broad that it is not only bound to the worldly caliphate; but actually it underlines Imam Ali's true caliphate and succession to the Holy Prophet Muhammad (PBUH).
Imam Ali (A.S) has all the authorities and powers that the Holy Prophet enjoyed and for implementation of God's commandment, the believers do honor him and consider him prior to themselves due to his knowledge and purity which has been confirmed by God and the Holy Prophet (PBUH).
All God's Hojjats after Imam Ali (A.S), from Imam Hassan (A.S) to the Promised Mahdi (A.S), are the same as Imam Ali (A.S). No matter how much people would respect or disrespect them, they are always God's Hojjat and Holy Prophet's successors on earth. Therefore, it is worthy not to rely on only Imamate whenever we talk about Imam Ali (A.S) and other Holy Prophet's successors; we'd better remember that they are Wali of Allah; that they have more right and priority over all believers; that they have knowledge, purity and justice; that they are God's best servants and that they enjoyed best behaviors among people. All these titles have special meanings and all these features are fully embodied in these holy Imams. Thus, it is better to use these titles along with the word 'Imam' in our speeches.
source : www.tebyan.net
