Sometimes I say prayers, typically tehillim, that appear to contain a promise to do something. Example: " חַסְדֵי יְהוָה, עוֹלָם אָשִׁירָה; לְדֹר וָדֹר, אוֹדִיעַ אֱמוּנָתְךָ בְּפִי. I will sing of the mercies of the LORD for ever; to all generations will I make known Thy faithfulness with my mouth."
When I say this, am I taking on a neder or a shevu'ah to sing of G-d's mercies forever? I believe the answer must be "no," since--among other reasons--many people say the entire book of Tehillim every month, every week, or every day, thus "swearing" to many such things on a regular basis, and it doesn't seem to be a problem. But exactly why isn't it?
(Is it because I do not actually have in mind to make the neder as I say the prayer? --But shouldn't I in fact honestly have in mind all I am saying in a truly sincere tefilla?)