Whether it be ethics or the Gospel, quoting Bible verses is rarely enough. Would you be persuaded on matters of ethics or salvation by a Muslim or Hindu quoting references from their holy books?
Yes, the Word of God never returns completely void but may return almost void at times if Christians do not explain the reason and purpose of what the Bible states.
Can you explain the Gospel? If not or to learn how to effectively do so using apologetics, please checkout Why Jesus in the sidebar.