Mesillat Yesharim.8
Mesillat Yesharim.8:1
The passage teaches that zealousness is acquired through the same means as carefulness, and that recognizing one's great obligation to God through contemplating His constant goodness and miracles—which every person experiences regardless of their circumstances—will awaken the heart to serve God diligently.
בְּדֶרֶךְ קְנִיַּת הַזְּרִיזוּת הִנֵּה הָאֶמְצָעִים אֲשֶׁר נִקְנֶה בָּם הַזְּרִיזוּת, הֵם הֵם אוֹתָם אֲשֶׁר נִקְנֶה בָּם הַזְּהִירוּת, וּמַדְרֵגוֹתֵיהֶם כְּמַדְרֵגוֹתֵיהֶם, וּכְמוֹ שֶׁכָּתַבְתִּי לְמַעְלָה וְאָמְנָם, מַה שֶּׁיּוּכַל לְהַגְבִּיר הַהִתְעוֹרְרוּת הַזֶּה הוּא הַהִסְתַּכְּלוּת בְּרוֹב הַטּוֹבוֹת, שֶׁהַקָּדוֹשׁ בָּרוּךְ הוּא עוֹשֶׂה עִם הָאָדָם בְּכָל עֵת וּבְכָל שָׁעָה, וְהַנִּפְלָאוֹת הַגְּדוֹלוֹת שֶׁעוֹשֶׂה עִמּוֹ מֵעֵת הַלֵּדָה עַד הַיּוֹם הָאַחֲרוֹן, כִּי כָּל מַה שֶׁיַּרְבֶּה לְהִסְתַּכֵּל וּלְהִתְבּוֹנֵן בִּדְבָרִים אֵלֶּה, הִנֵּה יַרְבֶּה לְהַכִּיר לְעַצְמוֹ חוֹבָה רַבָּה אֶל הָאֵל הַמֵּטִיב לוֹ,
The means through which Zeal is acquired are the same ones through which Watchfulness is acquired, and their levels are likewise similar as I wrote earlier. However, that which may intensify this rousing is looking into the many benefits that the Holy One blessed be He does with a man at all moments and times and the great wonders G-d performs for him from the time of his birth until his final day. For the more one looks into and contemplates these things, the more he will recognize his enormous debt to G-d Who bestows good to him.