Faith is defined in a practical way in Hebrews 11:1 “Now faith is the substance of things hoped for, the evidence of things not seen.”
The writer of Hebrews goes on for thirty nine additional verses to illustrate these who took God at His word and had faith in what He said.
Jacob, Gideon, and Samson were all to human in their failure, and even Abraham slipped up a few times. But they were believers.
What is faith? It is confidence that someone or something is reliable.
Paul puts the facts of faith in a nutshell. That Christ died for our sins according to the scripture; and that he was buried, and that he arose again the third day according to the scriptures I Corinthians 15: 3-4
Many people think Acts 16:31 is too easy and simple a method of salvation. “Believe on the Lord Jesus Christ, and thy shalt be saved and thy house.” Actually, simple believing is very hard for most people.
God does not want human boasting, so salvation is by grace, and through faith, not of works.
We must have faith to believe what God says in His Word.