You need to have a testimony. The Lord wants us to have a testimony. A testimony gives witness to the existence and character of our God. It is not good enough to say "I believe in Jesus because my parents did". A testimony is a moment when the Lord does something so big in your life that he leaves no doubt in you. A testimony is something to look back at and remember in moments of doubt. A testimony is the story you tell to those who do not have one as evidence of God's existence and love. He wants each of his children to have one.
The Lord gave a testimony to the entire nation of Israel when he rescued them from their slavery in Egypt. He knew that hardship would fall on them but he was going to use that suffering to give them a testimony that they would always look back at as a nation. It was that "wow" moment and he had planned it from the beginning:
I don't think there is a better passage in the Bible for summing up the purpose of the testimony he gives to us.
I accepted Jesus as my Saviour at the age of seven, according to my mother's faith but I did not know Jesus until I was 19 years old, when he gave me my testimony. He allowed me to escape into rebellion, to become enslaved by many things of this world. Then he mounted a rescue where he alone saved me from destruction, when he made himself known to me in a way I could never doubt. Regardless of what becomes of me or what the world may say, no one could ever rob me of the testimony I have been given.
As I watch my children face the perils of this world, some lost in rebellion, some questioning without a testimony, I do not fear. I know what the Lord is doing because he did it for me. He is working on their testimony and a moment will come for the "wow", when Jesus will leave no doubt in them as to who he is and how he loves and what he is inviting them into. The choice will always be theirs so my prayers are that they will decide for Jesus, but I know Jesus will present them with that choice.
Once you have your testimony don't ever let go of it. There will be more to follow but it is that first one that will see you through all that lay ahead of you. Share it often and remember it well. He planned it from the beginning.