"It is a grievous sin in the sight of God for any man to presume to baptize, unless God has authorized him by new revelation to baptize in his name"

This quote by Orson Pratt is stressing the significance of God's authority in the act of baptism. He is stating that it is a severe sin in the eyes of God for any male to baptize somebody unless God has actually particularly authorized him to do so. This is an important idea in Christianity, as baptism is a sacred act that signifies the cleansing of sins and the acceptance of Jesus Christ as one's rescuer. It is very important that the person carrying out the baptism is licensed by God to do so, as it signifies God's approval and true blessing. This quote is a suggestion that baptism is a sacred act that must just be performed by someone who has actually been given the authority to do so by God.