to make ready in advance, so that a person or event will be properly received when it arrives
At its core this is a simple, practical word: to get something ready ahead of time. You prepare a meal before guests sit down, a room before a traveler lodges, a road before a king travels it. The readiness always points forward to someone who is coming or something that is about to happen, which is why the word carries a sense of anticipation rather than mere busywork.
The New Testament keeps that one plain idea but stretches it across very different scenes. People prepare ordinary things: a Passover supper, burial spices, a guest room. John the Baptist's whole mission is described with it, prepare the way of the Lord, which turns the road builder's image into a picture of getting hearts ready for God.
Most striking is how often God is the one doing the preparing. He has already made ready a kingdom for the blessed and a fire for the devil, a city for the faithful, and gifts no eye has seen for those who love him. The same word that describes setting a table describes God arranging the future in advance. The shades differ by who prepares and for what, but the underlying action is the same: making ready beforehand.