The comments on 3 Nephi 12:7 suggested that “blessed are the merciful: for they shall obtain mercy” represented an expression that the way we act towards others will be a model for how God acts with us. That is the theme in these two verses. In the first, God forgives us when we are forgiving. The warning is in verse 15. If we are unforgiving, then the Father is unforgiving. The way we judge others will influence the way that God judges us.
This is also the theme from later in the Sermon on the Mount: “Judge not, that ye be not judged. For with what judgment ye judge, ye shall be judged: and with what measure ye mete, it shall be measured to you again” (Matthew 7:1–2).
This is not a verse telling us not to judge. Agency requires that we make judgments. It is simply a warning about the nature and quality of our judgments. It warns us that the way we judge others will be a model for how God judges us.