Genesis 6:5 - Matthew Poole's English Annotations on the Holy Bible

To the heart the Scripture commonly ascribes all men's actual wickedness, as Psalms 41:6 Proverbs 4:23, Proverbs 6:14, Proverbs 6:18, Jeremiah 17:9, Matthew 15:19 Romans 3:10, &c.; thereby leading us from acts of sin to the original corruption of nature, as the cause and source of them. Evil continually, i.e. that man was perpetually either doing or contriving wickedness; that not only his actions were vile, but his principles also; his very soul, yea, the noblest part of it, which might seem most free from the contagion; his mind and thoughts were corrupt and abominable, and so there was no hope of amendment.