Christians are taught to pray for everyone. Therefore when we plead the blood of Jesus over someone who may not be saved, they still benefit from those prayers. Since they benefit from our prayers they've unknowingly entered into a realm where they'll become exposed to the presence of God thus providing them with an opportunity to know about God, Romans 14:11 - As surely as I live, says the Lord, every knee will bow before me; every tongue will acknowledge God.
Those who claim to not believe in God rarely if ever turn down the blessings that He bestows upon them. Do we know of anyone who does not like when good things and/or people come our way, believers or not? That came by way of prayer. There may be some who say, "I don't pray!" well, if you speak, you pray. Words are prayers that are placed into the atmosphere, which command the universe to obey the prayers that we send out. This is why it is so important that we watch our words. We need to watch what we say to ourselves as well as to others, Psalm 38:12 - Those who want to kill me set their traps, those who would harm me talk of my ruin; all day long they scheme and lie.
This is why we're told to speak it into the atmosphere. For those who are still not convinced, just keep in mind that God does not function according to our belief system. Nor does He operate based on our limited capacity. For if that were true, we'd not have the moon, stars, dirt, oceans, the sky, the earth, other planets, animals, or other things that were not nor cannot be created by man.
Which leads into the thought of evolution. Let's go with the thought that humans evolved from animals, for a minute...God had to have made the first animal. God will not be not be mocked, Galatians 6:7-8 - Do not be deceived: God cannot be mocked. A man reaps what he sows. Whoever sows to please their flesh, from the flesh will reap destruction; whoever sows to please the Spirit, from the Spirit will reap eternal life.
His word will not return to Him void but will do what He has sent it to do whether we subscribe, refuse to believe, waiting for a sign, waiting until "we are ready", or just simply being, God is sovereign all by Himself. The sooner we realize that and operate in that fashion, the better off we'll become.