48 And when the Gentiles heard this, they began rejoicing and glorifying the word of the Lord, and as many as were appointed to eternal life believed.
Note that in God's realm of His sovereignty He has left a place for man's free will. He has not predetermined man's salvation outside of his foreknowledge. To do so would make man nothing more than a robot, or to force salvation down his throat so to speak.
What happened?
The Gentiles heard. Why?
Faith comes by hearing and hearing by the Word of God.
It was necessary that they hear the word of God in order that they be saved. This is not predetermined salvation/election. It is based on those that hear the Word and then having heard the Word make a choice whether to believe or not to believe. It is their choice. God does not force them to make this decision.
After they believed, (and speaking only of the ones that believed--there were no doubt some that did not believe), they rejoiced, and glorified, not only God, but the Word that they heard. Why? Because it was through the Word that they met Christ. Faith comes by hearing and hearing by the Word of God. Had they not heard the Word they would not be saved.
Had not the apostles been obedient and obeyed the Great Commission and gone to them they would not have been saved. It works both ways. It is our obligation to obey God and witness of the saving grace of God to give them the opportunity to hear it so that they might be saved. The choice is ours to obey God and be a witness for him or not to obey God and not witness. Their blood will be upon our hands. They will not be saved unless we go and tell them. They must hear the word of God in order to be saved. They glorified the word of God.
And as many as were appointed to eternal life were saved. The words ordained, and those words that speak of predestination always refer to the believer. They come after the person puts his faith in Christ. God knows who is going to be saved; we don't, and we ought not to presume to have the foreknowledge of God, therefore the entire point of the "elect" is moot for we cannot see what God sees. Our obligation is to go and tell others the gospel that they may hear and have the opportunity to be saved. And that is what that verse teaches.