גַּ֧ם אֶֽת־הָאֲרִ֛י גַּם־הַדּ֖וֹב הִכָּ֣ה עַבְדֶּ֑ךָ וְֽ֠הָיָה הַפְּלִשְׁתִּ֨י הֶעָרֵ֤ל הַזֶּה֙ כְּאַחַ֣ד מֵהֶ֔ם כִּ֣י חֵרֵ֔ף מַעַרְכֹ֖ת אֱלֹהִ֥ים חַיִּֽים׃ (ס)
你的僕人獅子也打死過，熊也打死過；這未受割禮的非利士人也必像牠們之一，因為他辱罵了活的上帝的軍隊。»
Shenei Luchot HaBerit
Another way of explaining our Psalm may be that David felt the need to apologize for taking credit for his humility, i.e. he apologized שלא גבה לבו, for having his humility become common knowledge. This in itself would rate as a form of boastfulness. He apologized, for not having remained silent, i.e. אם לא שויתי ודממתי נפשי. Whichever may be the case, the subject of this Psalm is the extreme importance of practicing humility.