This is a question and not the answer of oath (the statement which comes after the oath).
This is an affirmative question that confirms the issue in hand. It is stronger in presenting than just telling about it. Hence, Allah (swt) is stating the matter in a form of affirmative question because He knows very well that the person who possesses intellect and pure instinct would answer by “yes, there is”. So, this question makes the addressee confirm the matter instead of being informed about it and this is more affirmative than the answer of the oath sentence.
حِجْرٍ (perception): it is so -called in Arabic because it prevents its owner from doing wrong and this is the mission of the intellect, that is to restrict a person from doing evil and guide him to good until reaching the happiness and benefits.
Allah (swt) has willed the intellect in human beings as a means which guides the instincts, prevents them from transgressing and elevates them towards what Allah (swt) has willed for humans. This can be accomplished by following the deeds and instructions on man.
Anyone may ask: Why has Allah (swt) created these instincts in human beings?
The answer is: Because they have a very important job in our lives, so that Allah (swt) made them a part of human nature but these instincts have to be limited to what they have been created for, as for example, the instinct of loving food is created to preserve the life, the instinct of sex is found to retain the gender and the instinct of curiosity is the means of searching and investigating. Thus, the instincts are controlled by intellect and all the Quranic verses are addressing the intellect.