I John 3:16 NKJV
[16] By this we know love, because He laid down His life for us. And we also ought to lay down our lives for the brethren.

The Cross is a Witness of the ultimate alter, the ultimate sacrifice. Gentiles know the truth because of what happened on that day!

https://bible.com/bible/114/1jn.3.16.NKJV