To your point, many hold differing views of what blasphemy is and how it can affect our relationship with God. However, the considering the Bible and its context can point us in the best direction.
By definition, blasphemy is the anglicized form of the Greek word bla·sphe·miʹa. The Greek term basically means injurious, defamatory, or abusive speech and was used with reference to such speech whether directed against God or against humans. (Compare Re 16:11; Mt 27:39.) The English word “blasphemy,” however, is usually restricted to irreverent or abusive speech against God and sacred things. It is thus the antithesis of words of worship directed to the Divine Being.
Further, blasphemy includes the act of claiming the attributes or prerogatives of God, or ascribing these to another person or thing. (Compare Ac 12:21, 22.) The Jewish religious leaders accused Christ Jesus of blasphemy because he said that the sins of certain persons were forgiven (Mt 9:2, 3; Mr 2:5-7; Lu 5:20, 21), and they tried to stone him as a blasphemer because of his declaring himself to be God’s Son.
I hope that helps! To read more about blasphemy and other Bible terms, topics and doctrines, visit the website below. It contains hundreds of references that many have benefited from! :)