The Sufficiency of Scripture means that Scripture contained all the words of God He intended His people to have at each stage of redemptive history, and that it now contains all the words of God we need for salvation, for trusting Him perfectly and for obeying Him perfectly.
Throughout the Bible we see that the Scriptures provide everything we need to hear in order to bring us to Salvation. There is nothing more, no secret knowledge we need to stumble upon, than that is provided in the Bible (see 2 Timothy 3:15, James 1:18 and 1 Peter 1:23).
The Bible also contains everything we need to hear to equip us for living the Christian life (see 2 Timothy 3:16 and Psalm 119:1).
In these senses the Bible is sufficient.
There is an interesting discussion about the amount of scripture slowly increasing at each stage of redemptive history. Wayne Grudem argues that at each stage the amount of scripture available was sufficient.
This is why commands such as “you shall not add to these words” were able to be said by God as early as Deuteronomy 4:2). Of course, God has added to it as He has seen fit.
The sufficiency of Scripture also can encourage us to know that God has not spoken anything more that we need to believe, think or do, that is not already in the Bible.
Interestingly, our tendency to create additional rules for ourselves are met with failure and a lack of follow through, because the Holy Spirit does not empower us to fulfils our man-made rules. This was a problem Jesus addressed with the Pharisees (Matthew 15:3-7), but it is an issue we also must address in our own lives. The tendency to put ourselves under additional laws is very great.
Paul writes: “why…do you submit to it’s [additional] rules: ‘Do not handle! Do not taste! Do not touch!’? These rules…are based on merely human commands and teachings. Such regulations indeed have an appearance of wisdom, with their self-imposed worship, their false humility and their harsh treatment of the body, but they lack any value in restraining sensual indulgence.” (Col 2:20-23).
In my notes below I have also listed seven additional practical applications from this doctrine: