The flood of Noahs day was an unthinkable time of judgment of the sin of mankind (vv.57, 17, etc.), far outside the realm of our experience (9:11). In preparation for this devastating flood, Noah was to cover the ark both inside and out (and possibly even impregnate the wood) with pitch. This may have been a resinous sap, the residue of heating wood without allowing it to burn, an animal-derived glue, or some other concoction designed with the purpose of making the ark safe for its occupants. (An additional purpose may have been to help preserve the remains of the ark to the present day, and that one day it will be rediscovered; but that is as yet conjecture.) Those on board the ark were, to a great degree, kept safe from the waters of the judgment by the action of the pitch.
Interestingly enough, the Hebrew word translated pitch is translated elsewhere as atonement. Consider the following verse: For the life of the flesh is in the blood: and I have given it to you upon the altar to make an atonement [pitch] for your souls: for it is the blood that maketh an atonement [pitch] for the soul (Leviticus 17:11).
Such varied translation may at first seem unusual, but note the wonderful analogy. Just as those inside the ark were protected by the pitch from the judgment outside, so the one who believes may now escape the judgment of sin by the blood of our Savior Jesus Christ, through faith in its atoning power.
Much more then, being now justified by His blood, we shall be saved from wrath through Him. . . . by whom we have now received the atonement (Romans 5:9,11). JDM