The style of Lord Datta is to indirectly preach the people, who really need rectification in a specific line, by preaching directly the person, who does not need rectification in that specific line.
If you preach to a sinner regarding his sin, he will be hurt due to the basic inherent ego that is touched by your message. If you give the same message to a non-sinner in the presence of the specific sinner, your preaching will touch the sinner secretly without damaging his ego. The non-sinner will not be worried because he has not done that sin. The message will work as curing medicine in the case of sinner so that he will try to resist the sin from that day onwards.
The same message will act as preventive medicine in the case of a non–sinner also, who may face the same sin in future. Therefore, the medicine is not only for cure but also is for prevention. Hence, every message is useful to everybody either for cure or prevention.