Then he opened their understanding, that they might understand the scriptures. — It has been given to you to know the mysteries of the kingdom of heaven, but to them it has not been given. — I thank you, O Father, Lord of heaven and earth, because you have hidden these things from the wise and prudent, and have revealed them to babes. Even so, Father: for so it seemed good in your sight. — We have received, not the spirit of the world, but the spirit which is of God; that we might know the things that are freely given to us by God. — How precious also are your thoughts to me, O God! how great is the sum of them! If I should count them, they are more in number than the sand. — O the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out! For who has known the mind of the Lord? or who has been his counsellor? For of him, and through him, and to him are all things: to whom be glory for ever. Amen.
It is always and only the gift of the Spirit of God to understand the things of God. While many people point to the Bible (the Word) as the source of truth, the reality is that GOD is its source, and unless God speaks to you personally, you will not understand, because God is always understood by revelation. On the other hand, if you want to know Him, He is free with His gifts of understanding, and He Himself will walk with you and teach you. See 1 Cor. 2:11-13 (NIV): "no one knows the thoughts of God except the Spirit of God...We have... received the Spirit who is from God, so that we may understand what God has freely given us." God's truth comes to you because He speaks to you through His Spirit. Christians are always admonished to "Study the Word" (the Bible)--and so you should, but true understanding comes because God reveals Himself to you personally. It is the "unfolding" of His Word that gives light to the soul, and He is the only one who can do that. Ask Him to show you what He wants you to see, and always be open to what He says to you. He speaks to the open heart. As Jesus said, "He who has ears to hear, let him hear." Open yourself to Him and His truth, and you will have those "ears to hear."
PSA. 119:18. Luke 24:45. -Matt. 13:11. -Matt. 11:25,26. -I Cor. 2:12. ‑Psa. 139:17,18. -Rom. 11:33,34,36.