A "solemn pledge" is a sincere and serious promise. It is a commitment that carries a great deal of importance and is often made with utmost honesty and determination. Full definition
It concludes with solemn pledges of reform: «We want to denounce imperialism in all its forms and concomitantly pledge ourselves to work with native peoples in their efforts to recover their lands, their languages, their sacred traditions, and their rightful pride.... (firstthings.com)
To that connection we make the most solemn pledges, promising «to love, honor and cherish» each other «for richer. (religion-online.org)
He assured further that «in 2018, we will employ 2,000 more extension officers, with the solemn pledge of employing more graduates from our Colleges of Agriculture in the subsequent years.» (ghanapoliticsonline.com)