How do we know that new birth is necessary according to the Bible?

The necessity of being born again is a central teaching of Jesus, specifically articulated in John 3:7 where He states, 'Marvel not that I said unto thee, Ye must be born again.' This new birth is crucial because, in our sinful state, we cannot perceive or enter the kingdom of God. It is not a result of human effort but a work of God through the Spirit, as seen in Titus 3:5 which affirms that He saves us through the washing of regeneration. The new birth is the means by which God grants us faith and transforms our hearts to respond to His grace.