means,

Truly; in truth; in fact; certainly. Also, really; truly; with great confidence.

Jesus said,
"...Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. ... For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life..."
John 3:5-6 & 16