. . . . . . . . idea of helping . . . . . . . . man was unpleasant in itself.

The first blank is referring to the idea and the second to the man. For the first blank, the nature of the idea is specified that it is of helping somebody, thus definite article "the" will be used.
For the second blank, the man is specified that it is the man who needs help, thus definite article "the" will be used.