Thanks for your question.
The first explicit description of the character of God occurs in a revelation to Moses about 1400 B.C. Moses had received many communications from God during the events of the Exodus, but he evidently felt that he did not yet know God as a Personality, so he makes a request:
"if I have found grace in thy sight, show me now thy way, that I may know thee ..."
When God agreed to his request, Moses enlarges on it: "Show me thy glory". Now Moses had on more than one occasion already witnessed the "physical" glory of God in the form of great light and demonstrations of power. Here he wants something more. God is aware of this:
"I will make all my goodness pass before thee, and will proclaim the name of the LORD before thee ..." (Exodus 33:13-19).
The way, the glory, the goodness of the Lord will all be expressed in His Name and will enable Moses to "know" Him. This Name is now proclaimed:
"The LORD, the LORD God, merciful and gracious, longsuffering, and abundant in goodness and truth, keeping mercy for thousands, forgiving iniquity and transgression and sin, and that will by no means clear the guilty . . . " (Exodus 34:6,7).
So emerges the great portrait of the God of the Bible given by Himself. He has a definite moral character, in which mercy, longsuffering (slow to anger, R.V.), goodness and forgiveness play a great part, but always consistent with His "truth". Echoes of this description are frequently found in the subsequent books of the Old Testament, especially the Psalms (see Psalm 103, for example) and the prophets.
This portrait of God expresses His "goodness" and also His "glory" of character. It is this aspect Jesus has in mind when he declares to the woman of Samaria, "God is Spirit" (not "a Spirit" which misleads) (John 4:24). The character of God is described as "Spirit". It forms a great contrast with the natural character of human flesh expressed in its thinking and desires, and described by John as "the spirit of the flesh ... of the world ... of error".
The Holiness of God
It follows from what we have just considered that God in His nature and character is quite different from man. He dwells in "light unapproachable", unseen by mortal eyes, says Paul. But His "thoughts" (a term which always includes His purposes) are greater than man's, as he said:
"For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts" (Isaiah 55:9).
So God is "holy": that means He is "set apart" from mankind. Man cannot blunder heedlessly into His presence as if God were just another man. On account of their sins they cannot approach Him at all, except in the way He indicates. Israel were taught in the Law that approach in worship and sacrifice could only be through the priests, the sons of Aaron, whom God had Himself appointed. The aim of the Law was to develop in the people of Israel that mind and character which were like His. So He commanded them: "Be ye holy; for I am holy" (Leviticus 11:44); and Peter echoes this in writing to the early believers in Christ:
"But as he which called you is holy, so be ye holy in all manner of living" (1 Peter 1:15).
Jesus had already said as much to the woman of Samaria --
"The hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. God is Spirit: and they that worship him must worship him in spirit and in truth" (John 4:23,24).
In Old Testament times God had already revealed Himself as a "Father". "Israel is my son, my firstborn" (Exodus 4:22) was His declaration to Pharaoh in Egypt. Through the long centuries of their experience the faithful appreciated the relationship:
"Like as a father pitieth his children, so the Lord pitieth them that fear him. For he knoweth our frame; he remembereth that we are dust" (Psalm 103:13-14).
In the New Testament the supreme manifestation of God as Father is in the person of His beloved Son. Jesus constantly refers to God as "my Father" and, when addressing the disciples, as "your heavenly Father". The infinite grace of God, so dear to the psalmists and prophets, was shown in the giving of His Son as the atonement for sin. And so the faithful are granted a new relationship with God, in which they are not only "heirs with Christ" but "sons and daughters of God". John exclaims:
"Behold, what manner of love the Father hath bestowed upon us, that we should be called children of God: and such we are" (1 John 3:1, R.V.).
But in these days of casual familiarity it is easy to slip into the habit of thinking of God, and indeed even addressing Him, as "one of us". Jesus kept his priorities clear at all times, and particularly in his prayers. "I thank thee, 0 Father, Lord of heaven and earth" (Matthew 11:25) warns us that although God is truly our Father, He remains "Lord of heaven and earth" and should be worshipped as such. Twice in his prayer for the disciples shortly before his crucifixion, he addresses God direct: "Holy Father ... 0 righteous Father" (John 17:11,25). There is no familiarity here, but a profound recognition of this "otherness" from man.
Similarly the Apostle Paul, quoting from the Law and applying the saying to the believers in Corinth, urges them to "come out" and "be separate" from the idolatrous worship and practices in Greek society. God promises them, "I will be a Father unto you, and ye shall be my sons and daughters"; but Paul does not hesitate to complete the quotation, "saith the Lord Almighty", and to go on to urge his readers to cleanse themselves "from all defilement of flesh and spirit, perfecting holiness in the fear of God", that is, in reverent worship (2 Corinthians 6:17-7:1).