文字上:a silkworm will only stop producing silk when it dies; a candle will only stop "crying" when it turns into ash. 寓意上:I will only stop thinking of you when I die. I will only stop crying when I die/turn into ash
Till the end of life a silkworm keeps spining silk, till burning itself out a candle goes on lighting us. A spring silkworm may not stop spinning silk until death, a candle’s tears dry only when it is burned down to ashes.