Why preach the gospel to all if God has already chosen or preordained only a few individuals for salvation?

Scriptures have clear evidence that God has already chosen some individuals for salvation. Here are some references... "When the Gentiles heard this, they began rejoicing and glorifying the word of the Lord; and **as many as had been appointed to eternal life believed.**" (Acts 13:48) "And the Lord said to Paul in the night by a vision, “Do not be afraid any longer, but go on speaking and do not be silent; for I am with you, and no man will attack you in order to harm you, **for I have many people in this city**.” (Acts 18:9-10) "For those whom He foreknew, **He also predestined** to become conformed to the image of His Son, so that He would be the firstborn among many brethren; and these whom He predestined, He also called; and these whom He called, He also justified; and these whom He justified, He also glorified." (Romans 8:29-30) The above verses provide us ample evidence that God in His sovereignty chooses some individuals for salvation. Them He justifies and glorifies. Then we also see in the Scriptures... "And He said to them, “Go into all the world and **preach the gospel to all creation.** The one who has believed and has been baptized will be saved; but the one who has not believed will be condemned." (Mark 16:15-16) “For God so loved the world, that He gave His only Son, so that **everyone who believes in Him will not perish, but have eternal life.**" (John 3:16) According to the reformed theology how can the above both sets of verses be reconciled?