John 1:18

No one has ever seen God; God the only Son, who is in the bosom of the Father, he has made him known.

John 12:41

Isaiah said this because he saw his glory and spoke of him.

Treasury of Scripture Knowledge

Summary

And when Gideon perceived that he was an angel of the LORD, Gideon said, Alas, O Lord GOD! for because I have seen an angel of the LORD face to face.

Bible References

Because

John 1:18
No one has ever seen God; God the only Son, who is in the bosom of the Father, he has made him known.
John 12:41
Isaiah said this because he saw his glory and spoke of him.