In the poem Tsars or ("Kings"), Shevchenko is taking a satirical look at royal courts in general, presenting killing, debauchery, and adultery as being typical of their behaviour, and so allowing him to obliquely attack tsarism in particular.
The first example he presents is that of King David of Israel. One of the greatest kings of the Bible, he nonetheless committed adultery with Bathsheba the wife of Uriel the Hittite, and maneuvered Uriel to be killed (thus committing murder in some degree) to take Bathsheba as his wife. From Andrusyshen's translation, Shevchenko describes the events as:
Meanwhile Uriah slept; the poor dear fellow
Never suspected what was happening
In secret in his household — that the king
Had stolen from his home, not gold or silver
But the more precious treasure of his wife.
And that the husband might not know his loss,
The king just had him killed, and there’s an end! ...
What were the consequences of the king's conduct? David wrote one of the penitential psalms, Psalm 51, in response to Nathan criticising him, and the child who was born as a result of the adultery was killed by god. Following this:
David comforted his wife Bathsheba. He had intercourse with her, and
she bore a son, whom David named Solomon.
(2 Samuel 12:24-25).
So for David there were basically no consequences; a king can do exactly as he wants. Shevchenko further underlines the emptiness of David's response by saying that the tears he shed in public were "mendacious", and the psalm he was not even sincere, simply words to placate Nathan and the people:
Then the king shed a few mendacious tears
Before the people, wrote a brand-new psalm
To pull the wool over old Nathan’s eyes,
And happy once again, and drunk again,
He lavished his attentions on the lady.