Is the cake perfect and thoroughly furnished to become a cake with just the flour? "
Nope even though flour is profitable or useful for a perfect cake.
Is the doctrine, etc. perfect and thoroughly furnished with just scripture?
Nope, for the same reason. There's just no way to make profitable or useful mean "all that's needed" or "entirely sufficient."
Hebrews 10:10 By the which will we are sanctified through the offering of the body of Jesus Christ once for all. 11 And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins: 12 But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God; 13 From henceforth expecting till his enemies be made his footstool. 14 For by one offering he hath perfected for ever them that are sanctified. Sounds to me like everything needed for “perfection” is already found in scripture.
>> There's just no way to make profitable or useful mean "all that's needed" or "entirely sufficient."<<
"Most assuredly, I say to you, he who hears My word and believes in Him who sent Me has everlasting life, and shall not come into judgment, but has passed from death into life." (John 5:24)
1 Corinthians 6:11 And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.
Rom. 4:5, "But to the one who does not work, but believes in Him who justifies the ungodly, his faith is reckoned as righteousness,"
Rom. 5:1, "therefore having been justified by faith, we have peace with God through our Lord Jesus Christ,"
What more would you say is needed when scripture says we have it all?