13 The fire must be kept burning on the altar continuously; it must not go out.

13 Fire shall be kept burning on the altar continually; it shall not go out.

13 The fire shall ever be burning upon the altar; it shall never go out.

13 Remember, the fire must be kept burning on the altar at all times. It must never go out.

13 A fire shall always be burning on the altar; it shall never go out.

13 The fire must be kept burning on the altar all the time; it must not go out.

13 Fire shall be kept burning upon the altar continually; it shall not go out.

13 A continual fire shall be kept burning on the altar: it shall never go out.

13 The fire must always be burning on the altar. It must never go out. 

13 Fire must be kept burning on the altar continually; it must not go out.

13 A perpetual fire shall be kept burning on the altar; it shall not go out.

13 A perpetual fire must be kept burning on the altar; it must not be quenched.

13 The fire must be kept burning on the altar all the time. It must not go out.