As a child we believe most things our parents tell us without proof. If your dad told you spaghetti grew on trees, as a child you would believe him as much as when he told you that man walked on the moon. However, as a teen you want proof of that spaghetti tree. You want to see a picture of it and know what country it grows in. It is only natural to become a little more sceptical of things of which you have not received direct knowledge. It is no different with the things of Jesus Christ.
Some parents feel threatened when their teens start to ask questions and begin demonstrating doubts about what they have been taught as a child. Yet, this is a natural process. God is not a grandfather; he is a Father with many children. Each child must be born through faith in Jesus. This is not their parents' faith but their own. Some children grow into mature Christians with very little struggle and others have to work through a crisis of faith. Some will abandon the notion of God entirely and strike out on their own. Parents must pray but don't panic; God is allowing their child to gain a testimony. He needs them to receive their own revelation of him.
As a child it is natural to rest in your parents' faith but as an adult you need to gain your own revelation of God directly from God. Those who are called by Jesus are not called through any person. If each of us are open to God then we will receive direct knowledge of him from the Spirit and this will prove to be an encouragement to us during difficult times. Apostle Paul wrote to the Galatians:
I want you to know, brothers, that the gospel I preached is not something that man made up. I did not receive it from any man, nor was I taught it; rather, I received it by revelation from Jesus Christ. (Galatians 1:11-12)
This direct revelation is what lent itself to Paul's confidence and determination when things were rough. Sitting in jail he would be able to remind himself that he was in the will of God, doing what God wanted and nothing was going to stop him from being faithful to it. Even when the Jews turned against him and claimed he was teaching blasphemy, Paul was able to stay confident in the truth he had received directly from Jesus. Even when believing Jews went against this revelation and taught circumcision, Paul remained resolute to what he had received directly from the Spirit.
If you are a person who only knows Jesus through other people's testimonies you will find that your faith fades in difficult times, during trials and sufferings. Doubt creeps in rather easily when there is nothing of substance holding up your trust in Jesus. However, when you have received direct divine revelation as to the validity of the Word of God and the presence of the Holy Spirit in you then nothing in this world can dissuade you to turn away from Jesus. Nothing!
Receiving direct revelation through the Holy Spirit is not a difficult thing, it's just that we are often too lazy to seek it for ourselves. Jesus told us:
Ask and it will be given to you; seek and you will find; knock and the door will be opened to you. 8 For everyone who asks receives; he who seeks finds; and to him who knocks, the door will be opened. (Matthew 7:7)
If you want it, it is yours. Often our problem is that we seek it from different sources. We seek it through man but Jesus told us that it is ours directly from God and all we have to do is ask.
Don't live off your parents' faith any longer, or off of anyone else's either. Jesus wants you to have direct and personal knowledge of him. He wants a relationship with you directly, not through any other means. He wants you to be strong and confident in your faith and trust of who he is and what he has promised you. He wants you dependent on him and understanding the authority you have through him. He wants you to be available to him, to be involved in the mission, to be serving him the rest of your days on this planet. He wants you to be faithful in good and bad days, rejoicing in all things because you are confident of who you are and who you belong to. This is all yours in the confidence of direct revelation and it is available to you today.