"And he said unto me, Son of man, can these bones live? And I answered, O Lord thou knowest."–Ezekiel 37:3
The primary purpose of every true Gospel preacher is to glorify God, by exalting His Son, whether anybody believes or not. In many instances, the Lord allows his preachers to preach for some time in a desert place before ever seeing any conversions to Christ. Many times, the same word comes to the preacher's heart as what the Lord addressed to Ezekiel, "Can these bones live?" The answer is still the same, "O Lord thou knowest?" Why is it that only the Lord knows? The simple answer is that SALVATION IS OF THE LORD, Jonah 2:9.
God the Father knows those He has chosen to save in Christ– 2 Timothy 2:19, Nevertheless the foundation of God standeth sure, having this seal, The Lord knoweth them that are his.
God the Son knows those that the Father has given Him, and He laid down His life for them- John 10:14, I am the good shepherd, and know my sheep, and am known of mine.
God the Spirit knows those that the Father has chosen and that Christ has redeemed. His work is to regenerate these, in God's time, and bring them to Christ in saving faith. John 14:17, Even the Spirit of truth; whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.
Should this truth make us indifferent toward the unbelieving? God forbid! The Lord told Ezekiel to preach to the dry bones saying, "O ye dry bones, hear the Word of the Lord," Ezekiel 37:4. Then in preaching to them, He told Ezekiel to call to the Spirit in prayer to come and breath life into the dead bones, Ezekiel 37:9. This is the simple responsibility that the Lord has given his servants to do. We are not to go out and try to make converts ourselves. That would be no more than trying to patch together dead bones.
We must faithfully set Christ forth in truth, declare His righteousness as the sinner's only hope, and pray that the Spirit regenerate the hearts of sinners through the Word of Truth. This is the Word that sinners need to hear; the Word that God's elect will hear, Psalm 110:3.