Jesus made himself known after his resurrection. He appeared to many people showing that he was very much alive and in the flesh. There were witnesses to this truth; we do not only believe the testimony of one but of many.
How do you convince someone that the Bible is authentic? I’m continually saying that the Bible is the only truth, but how do we prove that it is God’s holy Word? There are many ways, but the easiest way is to rely on the Holy Spirit to convince.
Our best way to personally prove it is to live a life holy and acceptable to God and not conform to the world's standards. Jesus is our standard; though it seems high, we should strive toward that goal daily. It won’t be until we meet him that we achieve that goal, but in the meantime, we can enjoy the journey. The change others see in our lives will be the proof.
I appeal to you therefore, brothers, by the mercies of God, to present your bodies as a living sacrifice, holy and acceptable to God, which is your spiritual worship. Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect. Romans 12:1-2