Suffering unjustly has a way of increasing the weight of the suffering because self-pity can quickly fill the heart with bitterness on account of the wrong done to you. But Peter would have his readers know that the Lord gives strength to endure when one’s conscience is free of guilt before God.
Again, Joseph serves here as a vivid example. During his slavery and imprisonment, he embraced no bitterness on account of the wrong done to him (be it by his brothers, Potiphar, or the butler). Because his conscience was clear before God, he received from God grace to endure injustice. One might also think of David whose master, King Saul, sought to harm him (1 Samuel 18:6–16). His conduct and several psalms reveal the attitude that prevailed in his heart (though not without struggles of faith).
19 For this is a gracious thing, when, mindful of God, one endures sorrows while suffering unjustly.