Scripture contains many instances of these two opposites occurring together. Comparison of the passages suggests that, at least in many of the contexts, they refer to judgments passed, preferences and approval or disapproval expressed. Often those who "know" or "speak" good or evil are acting as people who assume or hold positions of authority. This should become clearer if we look at occurrences of the expressions in their contexts.
Abrahams unnamed servant has come to the home of Abrahams kinsfolk seeking a bride for Isaac. He has prayed that the Lord will guide him to a suitable bride, describing what kind of young woman this would be. He has met Rebekah at the well and she has met all the criteria which he had described in his prayer. Welcomed into her house by her brother Laban and the family, he has insisted on explaining exactly what his mission is and has detailed exactly what he had prayed and what Rebekah did to make him sure that she was the bride whom the Lord had chosen for Isaac. He asks what the familys response is to what he has said.
"Then Laban and (his father) Bethuel answered and said, the thing proceedeth from the Lord: we cannot speak unto thee bad or good. Behold, Rebekah is before thee, take her, and go, and let her be thy masters sons wife, as the Lord hath spoken" (vv.50-51).
In theory they could be saying that they could at the best say nothing, but they proceed to approve the match. Yet their words clearly imply that they are not in a position to be the judges, for they accept that "the Lord hath spoken". The best interpretation of their response is that they dare not seek to express official approval in the light of the way in which the Lord has already shown unmistakably that He approves. Laban and Bethuel admit that they cannot presume to permit or prohibit Rebekahs becoming Isaacs bride. "Speaking good or evil" is equivalent to "approving or disapproving".
Genesis 31.3, 20-24
The time has come for Jacob to return home from Labans house with his wives, his flocks and his family. His period of service as a servant of Laban has come to an end. He has served well and Labans flocks have prospered. In spite of all that Laban could do to prevent it, Jacobs own flocks have also prospered. Jacobs wives are willing to go with him because Laban has treated them in a miserly way. Jacob has a moral right to leave. But he also has a right to go because he has had a word of command from the Lord.
When Laban set out in pursuit of Jacob his mind was set on forcing Jacob to bow to Labans rights as head of the family. He would force him to return. Then God appeared to Laban in a dream and said to him, "Take heed that thou speak not to Jacob either good or bad" (v.24). If this means that God forbade him to speak a single word to Jacob he obviously disobeyed, for he did speak. But certainly he did not speak as he had intended to. He intended to speak as head of the house, father of his daughters and master of Jacob. But God had taken control of Jacobs movements and set him free from Labans service. If Laban dared presumptuously to give orders to Jacob he would have God to meet about the matter. What he was forbidden to do was to speak to Jacob as a master with authority to pass judgment and expect full obedience. Once again the Lord has spoken and men dare not express their approval or criticism as from a position of authority. Gods authority takes precedence over mens, however important they may think they are. It is on these terms that Laban accepts Jacobs right to leave and enters into a non-aggression pact with him.
Balak, king of Moab, has sought the help of the prophet Balaam to get a curse pronounced on Israel. Balaam has enough understanding to be reluctant to agree. When he does make pronouncements his words come out differently from what Balak asked. Balak rebukes him, saying, "The Lord hath kept thee back from honour" (v.11). Balaam protests, "I cannot go beyond the word of the Lord, to do either good or bad of mine own mind; what the Lord speaketh, that will I speak" (RV). The context is best served by interpreting this to mean that if Balaam is going to pass judgment on Balak, favourable or unfavourable, it will be Gods prerogative to determine the message. The issue is that God is the ultimate judge of even kings like Balak.
To be continued.