There is no absolute truth. You can’t be sure of anything!
Those who say that there are no absolutes are often very adamant about their belief. If they say that they are absolutely sure, then they are wrong because their own statement is an absolute. If they are not 100 percent sure, then there is a chance that they are wrong and they are risking their eternal salvation by trusting in a wrong belief.
God tells us that there is an objective, absolute truth that is not subject to man’s interpretations or whims, on which we can base our eternity. That truth is the Word of God (John 17:7)