A would-be disciple, who puts his hand to the plough and looks back lacks
Answer Details
The phrase "puts his hand to the plough and looks back" is a biblical allusion, and it means starting something and then giving up halfway. Therefore, lacking "total commitment" is the most fitting answer, as it implies a lack of dedication to the cause or task at hand. It means that to be a successful disciple or to succeed in any task, one must have complete dedication, focus, and the will to see it through to the end.