You can depend solely on the Holy Spirit, but only if you have the Holy Spirit, know the voice of the Holy Spirit, and do what the Holy Spirit wants you to do, which will include.... reading Holy Scriptures, if available, which the Holy Spirit supports us reading.
We must use all that we have. Some people have less to work with that others so that God may seemingly require less of them:
"But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more." Luke 12:48
Remember these verses:
"And Jesus sat over against the treasury, and beheld how the people cast money into the treasury: and many that were rich cast in much.
And there came a certain poor widow, and she threw in two mites, which make a farthing.
And he called unto him his disciples, and saith unto them, Verily I say unto you, That this poor widow hath cast more in, than all they which have cast into the treasury:
For all they did cast in of their abundance; but she of her want did cast in all that she had, even all her living." Mark 12:41-44
Some men of God in the OT likely had no written scriptures at all, such as Abel and Moses, yet did they not at times please God?
God's judgment of men is according to what He knows that He has given them.
The Holy Spirit was not given the task to "preach" the Gospel, man was. The purpose of scriptures contained in the Bible is this....
2Ti 3:16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
2Ti 3:17 That the man of God may be perfect, throughly furnished unto all good works.
How can a man be instructed in righteousness without the scripture? How can a man be corrected for errors in his life with out the Word of God?
How can man get faith for salvation if he never hears the Word of God? Faith comes by hearing the Word of God. The entire world is being held together by the power of his Word. The Word is everything, Without it we have no hope, and are without God.
All truth must be confirmed by three witness's, the Father, the Son (Word of God), and the Holy Spirit. If anyone of these is missing then we do not have truth, only some man made doctrine that has no power to do anything.
John 14:16; “I will ask the Father, and He will give you another Helper, that He may be with you forever;
John 14:17; that is the Spirit of truth, whom the world cannot receive, because it does not see Him or know Him, but you know Him because He abides with you and will be in you.
John 14:18; “I will not leave you as orphans; I will come to you.
John 14:19; “After a little while the world will no longer see Me, but you will see Me; because I live, you will live also.
John 14:20; “In that day you will know that I am in My Father, and you in Me, and I in you.
John 14:21; “He who has My commandments and keeps them is the one who loves Me; and he who loves Me will be loved by My Father, and I will love him and will disclose Myself to him.”
John 14:22; Judas (not Iscariot) said to Him, “Lord, what then has happened that You are going to disclose Yourself to us and not to the world?”
John 14:23; Jesus answered and said to him, “If anyone loves Me, he will keep My word; and My Father will love him, and We will come to him and make Our abode with him.
John 14:24;“He who does not love Me does not keep My words; and the word which you hear is not Mine, but the Father’s who sent Me.
John 14:25; “These things I have spoken to you while abiding with you.
John 14:26; “But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all that I said to you.
This is a somewhat controversial passage. First it seems that the Holy Spirit abiding in you is contingent on whether you keep the commandments or not.
(also see Acts 5:32; ) But it seems the Holy Spirit will teach us "all" things ( John 14:26; ) but He will also bring to "remembrance" the things Jesus said to us.
I agree with @Curtis above, the Holy Spirit cannot teach us what scripture means, if we don't know the scripture in the first place. Also the Holy Spirit can
only bring to "remembrance" that which we have already heard. If we never read it in the first place, we can't remember it.
I personally take "all things" to mean scriptural, spiritual things. I've never heard of anyone learning how to be a brain surgeon, rocket scientist
or computer technician from the Holy Spirit. I'm not saying He can't do it. But I believe as a rule He sticks to spiritual things.