The source of the vision most of us receive is through the Spirit by our calling. God gives it just as surely as He gave Paul's, but it is a gradually accumulating one in which the pieces that complete the picture are added through the normal processes of study, comparing, analyzing, and applying what we learn.
Consider how the revelation of God changes the course of a person's life. If those who killed Christ had the vision to know who He was, they never would have killed Him. Why? They would have had an entirely different perspective of the consequences of their actions. That foresight would have generated prudence in them, and they would not have permitted themselves to kill Him. Notice also how verse 9 shows us that what God has done gives us a perspective involving things not literally seen, yet in verse 10 they are nonetheless revealed.
Through the entire section concluding in verse 16, Paul tells us that, because of God's gracious action in giving us His Holy Spirit, He has predisposed, enabled, or granted us the foresight or vision to make right choices in spiritual matters. God's Holy Spirit gives us discernment as to where spiritual and moral choices will lead. This is wonderful, but something further must be understood. This quality, ability, or skill must be developed. It must grow. It does not instantly and miraculously appear upon conversion.