“guilt offering.” The Hebrew word can mean “guilt” (Lev. 5:2), or a “guilt offering” (Lev. 5:6-7). The verse has an important double entendre. The fool mocks at both guilt, which he denies, and the guilt offering that would atone for his guilt, which he thinks is unnecessary. In the Old Testament, fools mocked at both their guilt and the guilt offering; today they mock Jesus, who offered himself for them. In the end, God will mock the mockers (Prov. 3:34) and they will bear their punishment (Prov. 9:12).
“favor.” The double entendre in the first stanza of “guilt” and “guilt offering” is reflected in the second stanza as well. The Hebrew word can refer to a “good understanding” of the way to reconciliation (HALOT Hebrew and Aramaic Lexicon), or it can mean “acceptance,” “favor,” in the sense that one who offers a sacrifice or asks for forgiveness gets acceptance from God. Thus, the verse can mean, as it is translated in the REV: “Fools mock at a guilt offering, but among the upright is favor [in that their guilt offering is accepted]. And the verse can also mean: “Fools mock at guilt, but among the upright is good understanding [of their guilt. Which would lead to asking for forgiveness].
More fully expanded, Proverbs 14:9 means that the fool mocks at his guilt and the offering that would atone for it, while the upright have a good understanding of their guilt and their sacrifice and, humbly asking for forgiveness, are shown favor by God and accepted by Him.