I think it's a valid question from a position of any given skeptic.
I really don't buy the oversimplified answers like "If he didn't leave then Holy Spirit wouldn't come", Or "He left because the mission to spread the Gospel had to be fulfilled", or to "Prepare a place", again neither make a lot of sense in a scope what Christianity is and what it expects.
But these are some of the very things Jesus Himself said:
"Don’t let your hearts be troubled. Trust in God, and trust also in me. There is more than enough room in my Father’s home. If this were not so, would I have told you that
I am going to prepare a place for you? When everything is ready, I will come and get you, so that you will always be with me where I am. And you know the way to where I am going.” (John 14:1-4)
"But very truly I tell you, it is for your good that I am going away.
Unless I go away, the Advocate will not come to you; but if I go, I will send him to you."(John 16:7)
So how are these answers "oversimplified"? They are the very answers/explanations Jesus gave.
The question is whether this world is better if Jesus is there for all to be able to experience apart from some "feeling" or a book narrative? It wouldn't make Christianity to be so doubtable. Every Thomas out there could visit a 2000 year old dude with holes in his hands and believe.
Except then it wouldn't be a matter of faith, but fact. I think it likely that if He was here today all kinds of studies and experiments would be done, and where would that get us?
Why leave without a trace, and except leave the world with a story and a promise of hope.
But Jesus didn't leave "without a trace." He was very specific in the comfort and assurance He gave His disciples.
"If you love me, obey my commandments. And I will ask the Father, and he will give you another Advocate, who will never leave you. He is the Holy Spirit, who leads into all truth. The world cannot receive him, because it isn’t looking for him and doesn’t recognize him. But you know him, because he lives with you now and later will be in you.
No, I will not abandon you as orphans—I will come to you. Soon the world will no longer see me, but you will see me. Since I live, you also will live. When I am raised to life again, you will know that I am in my Father, and you are in me, and I am in you. Those who accept my commandments and obey them are the ones who love me. And because they love me, my Father will love them. And
I will love them and reveal myself to each of them.” (John 14:15-21)
And regarding the Holy Spirit:
"I have much more to say to you, more than you can now bear. But when he, the Spirit of truth, comes, he will guide you into all the truth. He will not speak on his own; he will speak only what he hears, and he will tell you what is yet to come. He will glorify me because it is from me that he will receive what he will make known to you. All that belongs to the Father is mine. That is why I said the Spirit will receive from me what he will make known to you.” (John 16:12-15)
It seems like a good excuse to mask the reason as to why Jesus is not here. "Well, he was here, but you've missed him by about 2000 years, BUT he's coming back soon... so just wait and read this book about him".
That isn't what we are left with at all, and the Bible is not just another book we read, it is the very written word of God. And in the Bible we read words of Jesus, such as:
Jesus replied, “All who love me will do what I say. My Father will love them, and
we will come and make our home with each of them. Anyone who doesn’t love me will not obey me. And remember, my words are not my own. What I am telling you is from the Father who sent me. I am telling you these things now while I am still with you. But
when the Father sends the Advocate as my representative—that is, the Holy Spirit—he will teach you everything and will remind you of everything I have told you."
"I am leaving you with a gift—peace of mind and heart. And the peace I give is a gift the world cannot give. So don’t be troubled or afraid. Remember what I told you: I am going away, but I will come back to you again. If you really loved me, you would be happy that I am going to the Father, who is greater than I am. I have told you these things before they happen so that when they do happen, you will believe." (John 14:23-29)
Then Jesus came to them and said, “All authority in heaven and on earth has been given to me. Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you.
And surely I am with you always, to the very end of the age.” (Matthew 28:18-20)
Perhaps there are other reasonable explanations, but what would these be? What do you think?
I think Jesus' own words are "reasonable explanation" enough. If we don't trust His explanation, whose will we trust?