I've met many who previously were Christians who have declared themselves atheists and I always wondered how it all happened.
What really made them go from saying "Jesus is Lord" to "There is no God"?
After getting saved, the believer starts learning the Word of God and the Bible shows us there are practices which the believer needs to imbibe and act out.
1Corinthians 14:1 gives us two practices
"Pursue love, and desire spiritual gifts, but especially that you may prophesy."
He gives us two practices:
1. Pursue love(we'll discuss later)
2. Desire spiritual gifts.
Many Christians don't know they are supposed to desire spiritual gifts. They think it's for Pastors. This practice is for every Christian.
1Corinthians 12:7 explains why it is so important to imbibe this practice.
"But the manifestation of the Spirit is given to each one for the profit of all:"
He calls spiritual gifts "manifestations of the Spirit"
The Holy Spirit is inside the believer and can't be seen by the physical eyes, the basic way to show what you carry inside you is through the "manifestations of the Spirit"
That's why he says "unlock by desiring spiritual gifts, the manifestations of the Spirit". By doing this everyone including the believer will see and know that God is with the believer(1Corinthians 14:25).
That will also prove to the believer and those around that God really exists.
The believer who becomes an atheists didn't stay in faith to the point of having the manifestations of the Spirit, because no one ever taught him/her the practice of desiring spiritual gifts.
Spiritual gifts were so important to Apostle Paul, to the extent he went all out to impart believers with spiritual gifts and he explains that having spiritual gifts makes a believer established in the faith.
For I long to see you, that I may impart to you some spiritual gift, so that you may be established—
Romans 1:11 NKJV
Any believer who has no spiritual gift is not established and can easily go back into the world.
Pursue love and desire spiritual gifts.
God bless you!