The apostle Paul was a man familiar with 4 major first century cultures. He was a Roman citizen, he was a Jew who spoke Greek as well as Hebrew, and he was a Christian.
The Garden of Eden had a river which parted into the headwaters of four other rivers. These rivers were the Pison, Gihon, Hiddekel and the Euphrates (Genesis 2:10 - 14).After Jesus was nailed and hung on a cross, Roman soldiers divided up his clothes into four parts (one for each soldier - John 19:23).
The four witnesses of God on earth are miracles, wonders, signs and the gifts of the Holy Spirit (Hebrews 2:4).
The number of times rainbows are referenced in scripture are four (Genesis 9, Ezekiel 1:28, Revelation 4:3, 10:1).
Ezekiel, prophecy and the number 4
In Ezekiel's well-known 'wheel in the middle of a wheel' vision (Ezekiel 1, 10) he sees four living creatures transporting a throne with four sides and four wheels. Each of the living creatures (likely Cherubim, a class of angels) has four faces (the face of a man, lion, ox and eagle) and four wings (1:6).
Later in the book that bears his name, Ezekiel is told to proclaim to Israel that an end is coming upon 'the four corners of the land' (Ezekiel 7:2). In chapter 14 the prophet is told by the Eternal to ask Israel's unrepentant elders to repent or else four sore judgments will come upon Jerusalem. They are the sword, famine, wild beasts or animals, and pestilence (14:21).
Additional information on the Biblical Meaning of 4
There are 4 gospel accounts of Jesus’ life and ministry. Each of these emphasizes a unique aspect of his sacrifice and ministry. Matthew's focus is on Christ being the son of David and a King. Mark highlights the suffering servant aspect of his ministry. John proclaims Jesus is the One and Only begotten Son of God. And Luke showcases him as the Perfect Man.