The masses of the heavenly bodies and with them the mutual gravitational attraction increase with increase in the velocity of expansion. If the velocity of expansion of the universe increases beyond a critical value, the masses of the heavenly bodies and consequently the mutual gravitational attraction between them will increase to such an extent, that the whole universe will collapse (the crunch). Scientists point out that the universe is closely balanced between run away expansion and violent collapse. Probably this is the balance hinted at through these verses.