This scripture is talking of the born-again man and referring to the baptism in the Holy Spirit with the evidence of speaking in tongues (1 Cor. 14:21).
One of the main lines of attacks of the devil against Holy Ghost baptism is to make the things of God look foolish and stupid to you. Once this happens, he will succeed in keeping you away from them because nobody wants to look stupid. In contrast, he works to make the things of Satan look innocent, e.g., demonic family cultural traditions, heroic characterization of occult and magic in modern movies, etc.
Therefore, when you begin to speak in tongues like a stammerer, the devil will come and taunt you, “… Do you even understand what you are saying…?” or “… Listen to every other person’s tongue sounding fluent, yours is rubbish. It is fake…” But Isa. 28:11 already says, with stammering lips and another tongue you will speak. Rather than allowing this to deter you, ignore the devil and continue praying in the Holy Spirit. There is nothing good in the devil, so, do not expect him to commend you for speaking in tongues anyway.
As inelegant and limited as your speaking in tongues may sound initially, that is the proof of your being baptised in the Holy Ghost. But then, you will have to develop a prayer language out of the stammering lips. Turning the stammering lips into a prayer language is your responsibility and not that of the Holy Ghost. You may restrict yourself to just the stammer for the rest of your life, but the Holy Ghost is full. It is like you having a tank full of water and the tap that brings water into your house is a very tiny tap that releases it in drops. The water tank is filled but depending on the degree of release in the tap, it could just be drops. Thus, if all you have got is the stammering, you have the real thing. Just keep at it and let it develop.
PRAYER: I reject every deception of the devil to make me abandon praying in tongues. I experience more flows of the Holy Spirit. Amen.
BIBLE IN A YEAR: Ezekiel 23:1-49, Hebrews 10:18-39, Psalm 109:1-31, Proverbs 27:13