God's word contains the answers to every important question of life. It contains everything we need to know to live a godly life and thus inherit everlasting life. There are many authorities to which worldly men appeal.
Some people appeal to themselves and some appeal to other men such as philosophers.
And His commandments are not burdensome. If we love God and Jesus, we must first consider their commands above all else in answering life's difficult questions. After considering the word of God as our first source of authority, Christians may appeal to other sources of authority as allowed by God. For example, God established governments to dictate morality in certain respects. But in other respects, God dictates moral behavior apart from government.