1 Samuel 15:26

Moreover, to distinguish still more clearly between them, we have, against the fear of office, a possible help in the law of obedience, inasmuch as God in his goodness rewards our faith, and makes a perfect ruler of the one who has confidence in him, and places all his hopes in him; but against the danger of disobedience I know of nothing which can help us, and of no ground to encourage our confidence.

28. What then does it mean that the prophet refused to bear the sin of the penitent king, except that he saw him not truly penitent? To whom he first responded with those words of rejection, because he recognized that the king would by no means be changed. By this steadfastness of the prophet, certain overly lenient priests of this present time are reproved, who are weak in their conduct yet bold in their recklessness. They can scarcely sustain themselves, yet dare to take up the burdens of others to be carried; they do not bear their own light burdens, yet subject themselves to unbearable ones. Behold, the mighty prophet fled from taking up the burden of the king's sin, so that the priest of the Church may fear and dread to undergo the weight of unbearable sins. For the most part, however, let him so take up the sins of others that he nevertheless permits the one by whom they were committed to weep over those sins he undertakes to expiate. Hence Samuel by no means promised to bear the king's sin, yet he mourned for him whom he had declared rejected. For concerning him it is written shortly after: 'Samuel mourned for Saul, because the Lord repented that He had made him king over Israel.' He did not indeed promise to bear the king's sin, so that the king would strive to weep over it himself. But nevertheless he wept for the one he had declared rejected, so that he might render the Lord favorable toward him. In the literal sense, indeed, when the prophet repeats the sentence, he shows the irrevocable sentence of divine justice by which the sinner is so cast away that he is never permitted to return to the hand of divine mercy. It can also be understood in another way, that he asks the prophet to return with him to worship the Lord. For holy men who do not abandon the Lord by sinning have no need to return to Him through repentance. […]

This may relieve many perplexed consciences, who think themselves obliged to do what they have said they would do, though they see just cause to change their minds. Hath rejected thee, &c. - But he does not say, he "hath rejected thee from salvation." And who besides hath authority to say so?

I have sinned . . . turn again with me, that I may worship the Lord--The erring, but proud and obstinate monarch was now humbled. He was conscience-smitten for the moment, but his confession proceeded not from sincere repentance, but from a sense of danger and desire of averting the sentence denounced against him.

I will not return with thee - I cannot acknowledge thee as king, seeing the Lord hath rejected thee.