Doth a fountain send forth at the same place sweet water and bitter?
Fountain - the heart: as the aperture [so opees (G3692), 'place'] of the fountain represents the month. The image is appropriate to the scene of the letter, Palestine, wherein salt and bitter springs are found. Though "sweet" springs are sometimes found near, yet "sweet and bitter" (water) do not flow 'at the same aperture.' Grace can make the mouth that 'sent forth the bitter' once, send forth the sweet: as the wood (typical of Christ's cross) changed Marah's bitter water into sweet.