For myself, I have always used the word "levels" because that is how it seems to work. Much like a glass (vessel) of water can be filled, or less full....or even over flowing. Many times we will notice that when we are the most repentantly humble to our Lord in prayer and worship, we notice that the Holy Spirit seems to work within us strongly.
In the scriptures we find that believers are told to be "filled" with the Holy Spirit. It is my belief that all believers are given the Holy Spirit as a deposit and are initially filled....but staying filled is part of our everyday relationship with the Lord. We need less flesh, more Spirit....and there would be all "degrees" or "levels" (my words) of this in each person at different times in their lives. The goal is to be Spirit filled at all times.
A good example would be Stephen as he was being stoned, was filled with the Holy Spirit. It's a time when the flesh is at it's weakest and most humble and God's Spirit manifests in such a way that even other people notice something is different about that person.
Of course you and I would probably disagree on how this comes about. You would probably say that it was God who made this happen....and I would agree, but I would add that Stephen surrendered himself to God and then God worked through him in a mighty way....God did not force Stephen to be filled with the Holy Spirit. It's through our close relationship with God that the Spirit works in a mighty way. Is God able to "force' us? Yes, because He is God and all powerful, but He finds pleasure in our desire to surrender our flesh and our desire to be filled with His Spirit.
I believe that the haughty or sinful flesh spurns the Holy Spirit within a believer. Such a christian, even though he has the deposit of the Spirit within them, will only manifest a certain degree of the working of the Spirit within them while in such a fleshy state of being.
Only when a believer stays in that state of flesh after tasting of the beauty of God and the Spirit and never repents and never asks God to help him change his ways, will the Holy Spirit be taken away from him....or in some christian beliefs....he never had the Holy Spirit to begin with. *Hebrews 6*
I believe that even if a christian has the least amount of the Holy Spirit working in them...they are destined to be saved if they endure to the end. Those that desire to be filled more, may find more help and comfort in this lifetime. Of course some may say that Stephen did not find help or comfort as he was being stoned.....but when I read the scripture, it seems to me that at some point as he was gazing into the heavens, he no longer felt those stones hitting him....he was too focused on Jesus and filled with the Spirit to feel his flesh any longer....he was preparing to go home. God was merciful.
*Hebrews 6:4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
5 And have tasted the good word of God, and the powers of the world to come,
6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
7 For the earth which drinketh in the rain that cometh oft upon it, and bringeth forth herbs meet for them by whom it is dressed, receiveth blessing from God:
8 But that which beareth thorns and briers is rejected, and is nigh unto cursing; whose end is to be burned.
9 But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak.
10 For God is not unrighteous to forget your work and labour of love, which ye have shewed toward his name, in that ye have ministered to the saints, and do minister.
11 And we desire that every one of you do shew the same diligence to the full assurance of hope unto the end:
12 That ye be not slothful, but followers of them who through faith and patience inherit the promises.