To learn the truth about the Bible, it helps to understand how God had His messages delivered to mankind. God called spokesmen to be both His mouthpieces and His scribes. These people were called prophets and apostles.
These spokesmen of God did not make things up as they went along. Some of them, like Jeremiah, tried to avoid the job altogether. But they were overwhelmed by the Spirit of God and had no choice but to reveal what God had spoken (Jer. 20:9; Amos 4:8; Acts 4:20).
One big proof of the Bible is that God prophesied so many events before they took place and then they came to pass. God deliberately revealed events before they happened so that false gods would not get the credit for His works (Is. 48:3-5). He also revealed that Jesus would be born of a virgin centuries beforehand (Is. 7:14).
God wanted humanity to believe the truth about the Bible so He carefully chose and prepared men to be his voice even from the womb of their mothers (Jer. 1:4-9; Gal. 1:15,16). And Jesus Christ told His apostles that the Holy Spirit would give them the power to be His representatives of the New Testament (Acts 1:8).
Is the Bible true? Throughout the Old Testament in particular, the prophets of God made sure the people knew their words were not there own. They constantly began their teachings and prophecies with statements declaring God as their source of information: "The LORD spoke" or "Hear the word of the LORD," for example. The apostle Paul certified that his gospel was not from men but by a revelation of Jesus Christ (Gal. 1:11,12).
Why believe the Bible? Moses revealed in scripture that God carved out the Ten Commandments with His own finger and commanded Moses to write down all the words He spoke to Him that comprised the Laws of the Old Testament (Ex. 34:1,27). The Bible says that all Israel recognized Samuel as God's prophet and that Samuel wrote down his words from God and added them to the Old Testament scriptures (I Sam. 3:20;10:25). The prophet Jeremiah tells how God told him to write the words God spoke in a book (Jer. 30:2). The apostle John said that his words were written so people would believe in Jesus for eternal life and John promised that his writings were true (John 20:30,31; 21:24,25).
God even had a method of preserving the Old Testament. The prophets were instructed to place their teachings and prophecies from God by "the ark of the covenant" or elsewhere in the holy temple. Over centuries of time, writings continued to be added as God used new prophets for His revelations to new generations of mankind (Ex. 25:8-22; Deut. 31:24-26; II Kings 23:1-25).
As additional proof of the Bible, the prophets and apostles credited each other's writings as the word of God. Many of the prophets, apostles... and Jesus Himself quoted the Law of Moses. The apostles proved that ancient prophets such as David and Isaiah prophesied the birth, death, and resurrection of the Messiah. Jesus also said that Moses, the writers of the Psalms, and the prophets spoke about Him before His coming and that He was there to fulfil their prophecies (Luke 24:25-27,44,45).
Another way that God's spokesmen answer our question, "Is the Bible true?" is by making comparisons between true and false prophets or apostles. Moses taught that we will know a true prophet by whether his prophecy comes true or if they tell us to go and serve other gods (Deut. 13:1-5; 18:21,22). Jeremiah and Ezekiel said that false prophets will speak lies in God's name or give false visions (Jer. 14:14; 23:16; Ezek. 13:1-9). Paul said that false apostles will be cursed for preaching another gospel (Gal. 1:8,9).
The bottom line is that the Bible speaks in its own defense. The truth about the Bible is clearly seen in the words that the spokesmen of God spoke and wrote, claiming that their words came from God. We each have to choose for ourselves. The apostles themselves cautioned us to believe the prophets in order to be in a relationship with God.
that you should remember the words which were spoken before by the holy prophets, and the commandments of us, the apostles of the Lord and Savior. - II Peter 3:2, WEB
Blessed is he who reads and those who hear the words of this prophecy, and keep those things which are written in it; for the time is near. - Revelation 1:3, NKJV
We can believe the Bible at face value.