Or HaChaim on Genesis 31:38/אור החיים על בראשית ל״א:ל״ח

1 זה עשרים שנה, וג׳ "These twenty years, etc." The reason Jacob mentioned "twenty years" was that a thief or swindler would be on guard for a relatively short time not to commit any crimes. It is not in the nature of thieves to control their natural inclination for a long period of time. Jacob therefore wanted to show that the fact he had not stolen anything for such a long period should have made it plain that he was not a thief by nature. He underlined this by the word עמך, with you; He meant you have had plenty of opportunity to observe me commit a misdemeanour. When did I ever do so?

2רחליך ועזיך, "your ewes and your she-goats did not miscarry." We have to explore what Jacob meant by citing this detail. If he merely wanted to call attention to his success in managing Laban's flock, this is not the appropriate place for such a comment. He also referred to אילי צאנך, וג׳, "the rams of your flocks, etc." Who would have suspected Jacob of eating those? Moreover, if no one had knowledge of Jacob doing any such thing previously, who would step forward after all these years to testify against him?

3Jacob contrasted his own behaviour with that common amongst other shepherds. They all steal and account for the missing numbers by attributing them to animals miscarrying, whereas in reality they appropriated such lambs for themselves. Jacob now cited the fact that he had never even claimed that any of Laban's ewes or she-goats had miscarried as proof that he could not have stolen any of these animals. He could therefore not be accused of having eaten any of these animals himself. All his success had been due to G'd who had not allowed a single miscarriage to occur in order that Jacob could not be suspected of dishonesty.

4The reason that he mentioned "the rams of your flocks" is to teach us that the Torah considers a male baby lamb already as a ram when it has only just been born. Perhaps Jacob referred to a legal point mentioned by Maimonides Hilchot Gezeylah chapter 2, according to which if someone stole a lamb and it developed into a ram (grew up while in the thief's care) the thief has acquired it [legally speaking, this means primarily that he is responsible for its wellbeing. Ed.], the original owners not being able to reclaim the same animal as compensation. This rule applies even when the owners had not given up hope of retrieving the same animal. Jacob told Laban that even when the circumstances would have been such that he could have legally kept an animal for himself, he did not avail himself of the legality of the matter but acted strictly according to what his conscience dictated to him as being correct moral behaviour. He could have returned lambs to Laban instead of fully grown animals; however he returned fully grown ones if perchance an accident had happened to one of the young animals under his care. He did not even "consume" the difference in value between a lamb and a fully grown ram.