Sound doctrine is very important to God, in His Word He directs us to teach it, & hold fast unto it ( 2 John 1:9-11, Titus 2:7, etc.). For that reason it should also be important to us & it needs to be guarded and contended for. (Jude 3-4, Rom. 16:17-18). More often people depart from the truth (apostasy) because they did not have sound doctrine as their basis.
We as Christians follow the teachings of Jesus (sound doctrine) that are found in the bible, unsound doctrine is the teaching that contradicts or disagree with the Word of God.