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.