Psalms 18:26 Kabbalah

עִם־חָסִ֥יד תִּתְחַסָּ֑ד עִם־גְּבַ֥ר תָּ֝מִ֗ים תִּתַּמָּֽם׃

With the merciful Thou dost show Thyself merciful, with the upright man Thou dost show Thyself upright;

Read kabbalistic (mystical) interpretation of Psalms 18:26: and classical mystical sources.