He may have been referring to Romans 1:20 ("For since the creation of the world God's invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that men are without excuse.") and 2:15 ("...since they show that the requirements of the law are written on their hearts, their consciences also bearing witness, and their thoughts now accusing, now even defending them.").
If you don't understand Jesus Christ, one of the persons of the trinity, your understanding of GOD is incomplete, which means you still are persisting in a rejection of what all of nature testifies in Romans 1, the truth that there is a God. Therefore, you are still guilty and under condemnation.
It is only liberal denominations that confess a non-Christian can be saved in this period of grace.
Common grace doesn't save.