He died once for all, but if Jesus has not been raised we are still dead. Since he was raised, the Spirit brought him back to life, the same way he brings us into new life. We are born again, with a life that was brought to us by God - we couldn’t earn it. You just have to look to Him and you will live, never die. Gospel.
Jesus physically appeared to people - his disciples so that they would believe. He explained how the whole Old Testament was really about Him. He wanted them to see Him, to hear Him, to touch Him so that he would be absolutely and completely real to them.
Why did Jesus ascend to heaven? So He can rule over the present age and the age to come. He had to rise to his seat of power and sit down. He is now resting form all of His work and ruling from the throne of both now and the future.