I was once a Christian, a very pious one.
Christianity is not pious or practicing, but personal. You might continue your exploration of the Bible . . . anywhere . . . and notice how the Bible gives personal attention to people who would not get such attention, possibly, in human history. God cares about each person, even the evil ones.
And we can see that the Bible shows that God is personally involved with people, communicating personally especially with His children. But God is not conceited; Jesus even spoke personally with Satan > Luke 4:1-13.
But do we listen? >
"swift to hear, slow to speak, slow to wrath" (in James 1:19)
There are people who are listening to their anger and arguing and complaining and unforgiveness and their own "logic"; so they miss the gentle and quiet and humble communication of Jesus.
So, yes, I am offering how we need to believe something because we know God Himself has shown it to us, and maybe even proven it in our lives . . . including proving how He does things with those who obey how He takes care of us.
"God resists the proud,
. But gives grace to the humble."
. . . . . . . . . . (in James 4:6, also in 1 Peter 4:6)
"Therefore", every one of us has God personally communicating with us - - - deeper than words >
by means of His grace which is the effect of His love in our character (1 Corinthians 6:17, Romans 5:5, 1 John 4:17) and His personal guiding (Isaiah 58:11, Proverbs 3:5-6) in our lives . . .
or in our ego stuff we are having a run-in with the personal communication of His resistance!!
Each of us has proof of this, in one way or the other, right now. But ones are in stubborn denial; "and we all need to become more humble and thankful."
I keep wondering about an after life, since his passing. If there is one, and if there is...what might a religious person tell an atheist in such a case?
It depends on who you are, what you would tell an atheist.
I might get to know the atheist and see what he or she is thinking and feeling. And then "tailor" what I say, to how I might help the person. If the atheist is becoming open to the possibility of there being God, I would offer that God does exist and He made us so He can have children to spend eternity with Him . . . since He is not going to die and just vanish from existence.
Or, if the atheist is in stubborn and even violent denial, I might say nothing but be patient and pray for him or her. But sometimes someone in nasty and stubborn denial asks questions, anyway; so I might just answer the person's questions, as well as I could, praying for God to inspire me. I might say something simple like, I experience there is God and I find that He has me believing in Jesus and the gospel and living after we leave this life; and His love lasts longer than this life. And I am satisfied with Him; He is better than only a belief, and He has done me more good, than I or other humans have done for me.
But I have needed much correction (Hebrews 12:4-11) so I can benefit from Him > He corrects me, Himself; He is this personal with me; so it is not about trying to do some self-production of my own "movie" of my own life!!

And He has me sharing with other children of God, and our Father has us helping each other as family; so lone-wolf logic and effort and games of word chess arguing with self-invented logic are not going to help < this is "why" people's logic has not brought them to God: because their way does not work.
The one thing that is objectively true, I personally think...is that no one knows, hence my agnostic leanings.
How can a human know what his or her physical senses can not detect?? But we understand that God knows and He has sent His own Son who has been in His
"bosom". He, Jesus, would know God and then be quite qualified to come here in the flesh and tell us, plus show us how He is in love.
"No one has seen God at any time. The only begotten Son, who is in the bosom of the Father, He has declared Him." (John 1:18)
This is very personal, how Jesus is in our Father's own
"bosom", where Jesus can know truly how our Father is, and be our faithful and trustworthy witness.