Clearly Peter and Paul are men of mercy, whether they received mercy, were filled with mercy or were mercifully given to us by God.
Consider the mercy they received. Question Paul himself, or rather listen to him freely confessing: I was a blasphemer and a persecutor and an unjust man, but I received mercy. And he rightfully said: The saying is sure and deserving of full acceptance that the Lord Jesus came to save sinners of whom I am the foremost. Accept this example of confidence and consolation in blessed Paul that, now converted to the Lord, the awareness of your past transgressions may not grieve you excessively, but only humble you, as was the case of him who said: I am the least of the apostles, unworthy to be called an apostle because I persecuted the Church of God. Let us be humbled in this way under the mighty hand of God, and let us have confidence because we too have received mercy, we have been washed, we have been sanctified. And Paul’s example is for us all, because we have all sinned and are in need of God’s glory.
I have another example in blessed Peter to present to you. It is the more precious because it is so rare; and so sublime because of its uniqueness. Paul sinned, but he acted ignorantly in is unbelief; Peter had eyes open when he fell. Let us not lose hope for such a sinner, so long as he is willing to rise up again quickly.
You have heard how our Apostles received mercy, so that now none of you need to be unnecessarily confounded about his past sins and pricked by them on the bed of his conscience. Why not? Perhaps you sinned in the world, but did you sin more extensively than Paul. If you have sinned in the religious life, did you sin more than Peter? Yet by doing penance with all their heart, they received not only salvation but also holiness.
Bernard of Clairvaux, Sermon 3 for the Feast of the Apostles Peter and Paul (CF 53, pp. 110-112)