הָל֞וֹךְ וְאָמַרְתָּ֣ אֶל־חִזְקִיָּ֗הוּ כֹּֽה־אָמַ֤ר יְהוָה֙ אֱלֹהֵי֙ דָּוִ֣ד אָבִ֔יךָ שָׁמַ֙עְתִּי֙ אֶת־תְּפִלָּתֶ֔ךָ רָאִ֖יתִי אֶת־דִּמְעָתֶ֑ךָ הִנְנִי֙ יוֹסִ֣ף עַל־יָמֶ֔יךָ חֲמֵ֥שׁ עֶשְׂרֵ֖ה שָׁנָֽה׃
’Go, and say to Hezekiah: Thus saith the LORD, the God of David thy father: I have heard thy prayer, I have seen thy tears; behold, I will add unto thy days fifteen years.
Read kabbalistic (mystical) interpretation of Isaiah 38:5: and classical mystical sources.