1. This verse (6:159) means something completely different from what seems from your question. شيعا means different groups following different leaders, which is totally different from the word Shi’a which means the followers of the Prophets and their real successors.
2. Shi’a in Arabic language means the followers, who can be followers of true leader, so they are the real believers, or can be following a wrong leader, then they will be mislead.
3. Allah (SWT) Has Granted the title Shi’a to His best servants as you can read in Sura Al-Saffaat after mentioning the Prophet Noah, the mention of Prophet Ebrahim ( And Ebrahim was from his Shi’a) (وإنَّ مِن شِيعَتِهِ لَإبراهيم.
4. Allah (SWT) mentioned in Sura Al-Qassass about Prophet Musa and his followers and his enemies. He called the followers of Musa as his Shi’a and the opposite people as his enemies. Al-Qassass, verse 15.
'5. Shi'a is a title granted by Allah, The Glorious, to the sincere followers of the Prophets.
6. Shi'a Muslims are the real followers of the Prophet Muhammad (SAWA) through following his Progeny Ahlul Bayt (AS) which was been ordered by Allah and the Prophet (SAWA).
7. The Prophet Muhammad (SAWA) has repeatedly called the most sincere believers as "Shi'a of Ali" as you can read in many Sunni books of Hadeeth like
1. Shawaahid Al-Tanzeel by Al-Haakim Al-Hasakaani , V. 2, P. 356.
2. Kufa Ayat Al-Talib by Al-Kanji Al-Shafi'ee, P.244.
3. Al-Manaaqib by Al-Khawarizmi Al-Hanafi , P. 62.
4. Al-Fosoul Al-Muhimmah by Ibn Al-Sabbagh Al-Maliki , P. 126
5. Ibn Asaakir in Tareekh Dimishq 2:442.
6. Al-Khateeb Al-Baghdadi in Tareekh Baghdad, V.12, P. 289.
7. Al-Tabarani in Al-Mo'jam Al-Waseet, V. 6, P. 354.
'Wassalam.
