at SN 48.9 & 10, buddha taught the practitioner develops jhana by making letting go (relinquishment; abandonment; vossaga) the sole object. when jhana occurs, feelings of rapture & bliss manifest, which, on that level of samadhi, form the basis of the 2nd Satipatthana so what is the difference? for me, using effort is not letting go. by using effort, the mind can suppress. by suppressing, there can be limited spaciousness for the mental formations stored within the physical body to rise up, dissolve & purify