Jesus Christ died. He was buried. He rose the third day.
He was seen by many and diverse witnesses.
For I delivered to you as of first importance what I also received, that Christ died for our sins according to the Scriptures, and that He was buried, and that He was raised on the third day according to the Scriptures, and that He appeared to Cephas, then to the twelve. After that He appeared to more than five hundred brethren at one time, most of whom remain until now. (1 Corinthians 15:3-6)
When the Bible says, "We walk by faith, not by sight" (2 Corinthians 5:7), it does not mean that there never were any visible evidences. Nor does it mean that there are no visible evidences today.
The heavens are telling of the glory of God [today!]; And their expanse is declaring the work of His hands. (Psalm 19:1)
Since the creation of the world [even to this day!] His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made. (Romans 1:20)
In the first generation of believers, God did not think he was contradicting the grounds of faith by giving visible appearances of the risen Christ, and then later by confirmations of the word of truth in signs and wonders.
To [the apostles] He also presented Himself alive after His suffering, by many convincing proofs, appearing to them over a period of forty days and speaking of the things concerning the kingdom of God. (Acts 1:3)
After [our great salvation] was at the first spoken through the Lord, it was confirmed to us by those who heard, God also testifying with them, both by signs and wonders. (Hebrews 2:3-4)
What then does Paul mean when he says, "We walk by faith and not by sight"? As usual, the context is the key.
While we are in this tent [that is, the body], we groan . . . [longing for] what is mortal [to] be swallowed up by life. Now He who prepared us for this very purpose is God, who gave to us the Spirit as a pledge. Therefore, being always of good courage, and knowing that while we are at home in the body we are absent from the Lord - for we walk by faith, not by sight. (2 Corinthians 5:4-7)
Yes, Christ was seen once, with physical eyes. Yes, he did signs and wonders infallibly with a single word or touch. Yes, he died, and rose, and appeared to many. But NOW he is gone from sight. We do not see him that way now. As Paul says, "[When we are] at home in the body, [we are] absent from the Lord!" That is, we don't see him now. Not only that, in this body of ours, we groan. That is, we do not even see the full effect of his power in our lives now. Rather, Paul says, we have his Spirit as a pledge. The Spirit is an unseen, but experienced, downpayment, in advance of the sight of Christ in glory.
So in what sense then do we walk by faith and not sight? We walk by faith and not sight, because on the basis of the past, visible acts of God in Christ, and because of the compelling testimonies to these acts in the apostles, we now trust in this living Christ and what he promises to be for us, though we do not now see him. Paul says it like this in Romans 8:24-25: "In hope we have been saved, but hope that is seen is not hope; for who hopes for what he already sees? But if we hope for what we do not see, with perseverance we wait eagerly for it."
Peter puts it like this: "Though you have not seen Him, you love Him, and though you do not see Him now, but believe in Him, you greatly rejoice with joy inexpressible and full of glory" (1 Peter 1:8). I have never seen the risen Christ in the flesh. But his Spirit has enabled me to see his self-authenticating glory in the Biblical witnesses. The Christ that I see there, has won over my mind and my heart. So I say with Paul in Galatians 2:20, "I live by faith [not sight] in the Son of God who loved me and gave himself for me."
Walking by faith (for now) with you,