My reaction to the title of this thread is that what if you don't need yourself to have been a Christian to partake of the kingdom of God? Is it hard to believe there are righteous people of other religions?
You are right there are righteous people of other religions and atheists and people that do not believe in the Deity of Yeshua that are good people and in the end they will be in Hell. One of those trophies on Satan's shelf. Hell's fire for eternality. And there is salvation in no one else; for there is no other name under heaven that has been given among men by which we must be saved. Acts 4:12
Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me. John 14:6
Jesus answered him, “Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God.” John 3:3
For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life. For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him. John 3:16-17
Whoever believes in the Son has eternal life; whoever does not obey the Son shall not see life, but the wrath of God remains on him. John 3:36
I told you that you would die in your sins, for unless you believe that I am he you will die in your sins.” John 8:24
In him we have redemption through his blood, the forgiveness of our trespasses, according to the riches of his grace, Ephesians 1:7
Enter by the narrow gate. For the gate is wide and the way is easy that leads to destruction, and those who enter by it are many. For the gate is narrow and the way is hard that leads to life, and those who find it are few.
Matthew 7:13-14