Thanks, for quoting a scripture with your post, which you seldom do.
John 6:47 is true, as are all of the scriptures, but they must harmonize, if you are to understand the truths contained in the doctrine of Jesus. 1 Cor 2:14 says that the natural man cannot discern the things of the Spirit, and thinks them to be foolishness, so John 6:47 does not harmonise with 1 Cor 2:14, with the theory that the natural man is the one that can believeth in the things of the Spirit.
Those, in John 6:47,. who believe, are those that are able to hear our spiritual God's voice, as indicated in John 10:26-28., which will harmonize with John 6:47. God's sheep are his regenerated children.