I think that there is a level of certain commitment evident in this poem. I think that the certainty is because the speaker is committed to the idea that there are not two individuals in love, but rather both voices have merged into one. The speaker reiterates this theme several times over: "Let us possess one world; each hath one, and is one" and "If our two loves be one, or thou and I/ love so like that none can slacken and none can die." The level of certainty is present when one fully immerses their identity within another. The reason behind this might lie in Donne's metaphysical belief that perfection, or the achievement of the highest representation of love is possible. Donne does believe in the Platonic ideals or, forms, that indicate all of reality is a constant striving for the ultimate and pure nature of things. This drive to achieve the form presumes that an idyll is real, and perhaps, the commitment of the speaker in his love might be a method of expressing this; his love is the realization of the form of love. This drive is beyond certain, for it is absolute in its essence.
Donne's poem 'The Good Morrow' consists of three verses. Verse1 refers to the past; verse2 refers to the present; verse3 looks forward to the time future. Having awakened to a new morning of consciousness('And now good morrow to our waking souls'), the poet-lover looks back into the past, into those mundane and grossly physical, rather childish experiences, mistaken for love('sucked the country pleasures childishly'). Waking together and greeting their newly-awakened souls, the poet-lover realises how they had been in a state of deep slumber like the 'seven sleepers' of Ephesus. The certainty in the language and tone of the lover is due to a spiritual awakening, a new consciousness that is critical and introspective. Love is not mere bodily enjoyment; such enjoyment rather proceeds from spritual slumber. Love is the perfect union of two souls being fused into one. Critical examination of the past, recognition of the errors made, and an assured assessment in the present--these are all a necessary prelude to the metaphysical journey towards the future perfect.