The goal to form this group by Turkey is first to gather different small militant groups under one flag and make them official as a united military force that is recognized and supported by a NATO country, i.e., Turkey.
Second is that Turkey is accused of being passive in fighting terrorists of Tahrir al Sham several times by Syria and its allies; so, by trick of forming a new group, Turkey is trying to reduce the political and media pressure on itself and show that by forming this group, they are fighting against Tahrir al Sham terrorists; thus prevents Syrian Army possible operation in northwest of Syria.
Nevertheless, it seems that this trick is too late and the promise has given by Syrian-Iranian-Russian alliance to clear northwest of Syria specially Idlib province and by transporting heavy equipment to north of Syria and gathering troops, every day we approach the hour zero of the operation.
Therefore, recently Turkey proposed Tahrir al Sham to join the newly formed group in north of Syria to remove the problem of north of Syria and Idlib province.
One primary objective of the operation by Syrian Army and allies is presence of terrorist group related to al Qaeda such as Tahrir al Sham.
By declining Turkey’s offer by Tahrir al Sham, it seems Turkey’s final efforts to prevent the operation in Idlib has been defeated.