Is Tawassol (recourse) allowed in Islam? (Shia view)

Allah, the exalted, says in the Noble Quran as such: > وَالَّذِي هُوَ يُطْعِمُنِي وَيَسْقِينِ ﴿٧٩﴾ وَإِذَا مَرِ‌ضْتُ فَهُوَ > يَشْفِينِ ﴿٨٠ > > > "And it is He who feeds me and gives me drink; and when I am ill, it is > He who cures me" > > (**Surat Ash-Shu`arā,verse79-80 **) So, according to this verse we should ask our wills from Allah and we can simply ask them directly from Allah, what is the need of tawassol to holy men? Why some Muslims (Shia) call the name of some holy men with the intention that he will recourse in front of Allah for them? Is tawassol allowed in Islam?