I reject external ceremonial honor and false devotion; I offer only internal obedience, pure oblation, mutual love unmixed with calculation.
The speaker rejects the performance of honor: bearing 'the canopy' (the ceremonial tent of state), 'extern the outward honouring.' He dismisses those who lay 'great bases for eternity'—monumental investments meant to confer permanence—as building structures that prove 'more short than waste or ruining.' The speaker has seen 'dwellers on form and favour' lose everything by 'paying too much rent / For compound sweet.' Outward ceremony and monumentality are revealed as temporary and expensive performances.
Instead, the speaker offers to 'be obsequious in thy heart'—a radical privacy of devotion. The oblation is 'poor but free,' 'not mixed with seconds' (not adulterated), 'knows no art' (calculation). It is pure 'mutual render, only me for thee.' This is love stripped of ceremony, politics, monumentality. The couplet then addresses a 'suborned informer'—presumably time, fortune, or slander—claiming that a 'true soul / When most impeached, stands least in thy control.' Pure devotion becomes invulnerable to external accusation.
You could hold a grand public gesture—post about them, announce your love, make it official. But instead you choose quiet, persistent internal commitment that no one witnesses. It's the opposite of performing love; it's living it.