This question is quite a big one to unpack.
Our whole belief system is in fact based off of, Creation, The Fall, And Jesus' Life and Resurrection. Jesus' Life and Resurrection is such an important part because after the fall to repent from our sins we had to make a sacrifice and Jesus' death was that ultimate sacrifice.
If Jesus was never resurrected, we wouldn't be able to experience a closeness to God. Because when Jesus was resurrected, he paid the price for our sins. And when he was resurrected the Holy Spirit came.
But it also becomes bigger than that.
We know Jesus was a man who walked the earth, but if he only died that would make him merely a prophet that became a martyr. Our whole belief system would be changed because either God isn't real or we are still waiting for him to send his son which was prophesied in the Bible.
To be a Christian is to have faith. Faith that God is real and that he did send his son to die and be resurrected. So I want to conclude with my favorite quotes from Lecrae.
” If I am wrong about God, then I wasted my life. If you’re wrong about God, you wasted your eternity.”