The parliamentary system of executive vests many powers in the legislature for controlling the executive. Why, do you think, is it so necessary to control the executive?
The modern executive is a very powerful institution of government that enjoys greater powers compared to other organs. This generates a greater need to have democratic control over the executive to prevent the misuse of such extensive powers.
The makers of our Constitution thought with foresight that the executive must be put firmly under regular supervision and control. They wanted a government with a strong executive branch, but at the same time, enough safeguards were necessary to check against the danger of personality cult.
Control over the executive is essential to ensure that the government would be sensitive to public expectations and would be responsible and accountable to the people. The parliamentary system ensures that the executive will be answerable to and controlled by the people's representatives.
The most important feature of parliamentary executive is that the executive is routinely under the control and supervision of the legislature. The Council of Ministers is collectively responsible to the Lok Sabha, which ensures that the executive cannot become unresponsive.
This control mechanism ensures that the three organs of government work in coordination and maintain a balance among themselves, as the Constitution envisages.
Explanation
This answer draws directly from the textbook context which explains why controlling the executive is necessary: the executive enjoys greater powers than other organs, there's a need to prevent personality cult, ensure accountability and sensitivity to public expectations, and maintain constitutional balance. The parliamentary system was specifically chosen to enable this control through mechanisms like collective responsibility.