Musar do Psalmów 15:2

Therefore, every man who reflects should try with all his might to attain the final good, for if a man reaches a good state or elevation then he will always desire to ascend to the degree which is higher until he will finally attain the ultimate good and in this manner he will reach the "world of reward" which is the world to come. Long ago David longed to attain the good of the world to come, when he said: "Oh, how abundant is Thy goodness, which Thou hast laid up for them that fear Thee" (Ps. 31:20), and he said: "They are abundantly satisfied with the fatness of Thy house, and Thou makest them drink of the river of Thy pleasures" (Ps. 36:9). And this degree no one can attain except he be worthy of it, as he said: "Who shall sojourn in Thy tabernacle? Who shall dwell upon Thy holy mountain? He that walketh uprightly, and worketh righteousness" (Ps. 15:1). And the rest of the matter which is said there.

And "[I have returned to Zion, and will dwell in the midst of Jerusalem:] and Jerusalem shall be called the City of Truth" (Zecharia 8:3) - to magnify its importance. And our sages of blessed memory said (Makot 24a): "'who speaks truth in his heart' (Tehilim 15:2), like Rav Safra..." To teach you just how far-reaching the obligation of truth extends.