If all are called and few are chosen, and none can come unless called – why are we to testify and witness?
Because God in His Wisdom has seen fit to communicate to the human race by empowering believers with the Holy Spirit to proclaim God’s Word to our fellow humans. For example, the Lord opened Lydia’s heart in Acts 16:14 , but Paul spoke the words she needed to hear. Isaiah 6 is another good example. The Lord said “whom shall I send, who will go (to the nation of Israel) for us?” Isaiah answered “send me.” Romans 10: 14,15 & 17 – How shall they call on him in whom they have not believed? And, how shall they believe in him of whom they have not heard? How shall they hear without a proclaimer? How shall they proclaim except they be sent? (Remember Isaiah?) So then, Faith cometh by hearing and hearing by the word of God. The call to salvation is extended to everyone. But, salvation comes only to those who are willing to believe.