Protestant Laird

What does the bible mean when it says the letter killeth?

Also:

Ga:5:4: Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace.
Ga:5:5: For we through the Spirit wait for the hope of righteousness by faith.
Ga:5:6: For in Jesus Christ neither circumcision availeth any thing, nor uncircumcision; but faith which worketh by love.
Ga:5:7: Ye did run well; who did hinder you that ye should not obey the truth?
Ga:5:8: This persuasion cometh not of him that calleth you.
Ga:5:9: A little leaven leaveneth the whole lump.Ga:5:10: I have confidence in you through the Lord, that ye will be none otherwise minded: but he that troubleth you shall bear his judgment, whosoever he be.
Ga:5:11: And I, brethren, if I yet preach circumcision, why do I yet suffer persecution? then is the offence of the cross ceased.
Ga:5:12: I would they were even cut off which trouble you.
Ga:5:13: For, brethren, ye have been called unto liberty; only use not liberty for an occasion to the flesh, but by love serve one another.
Ga:5:14: For all the law is fulfilled in one word, even in this; Thou shalt love thy neighbour as thyself.
Ga:5:15: But if ye bite and devour one another, take heed that ye be not consumed one of another.
Ga:5:16: This I say then, Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
Ga:5:17: For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.
Ga:5:18: But if ye be led of the Spirit, ye are not under the law.

But, if I clearly taught elsewhere that repentance/belief alone was sufficient no one would think coming forward is necessary for salvation,or water baptism is necessary for salvation.