what is the purpose of a demon(s) possessing an individual?
I think one of the purposes is to
serve them (like a slave serves a slavemaster).
First a person is bought, like what the Devil attempted with Christ, Matt 4.9-10,
And saith unto him,
All these things will I give thee, if thou wilt fall down and worship me. Then saith Jesus unto him, Get thee hence, Satan: for it is written, Thou shalt worship the Lord thy God, and him only shalt thou serve.
There are people who are bought off with
these things and fall and worship and end up serving Satan.
In the dark realm the Devil or Satan (a spirit) buys off people (‘sell soul to devil’). Being bought therefore they are a possession. Being a possession they are therefore possessed. Being possesed, Satan (or one of his demons, fallen angels, spirits) has the ability and right to indwell what is possessed and to require further worship and service (I would think under compulsion).
All these spiritual happenings are
copied from the realm of Light to steal what is due God.
1 Cor 6:20 For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God’s.
1 Cor 7:23 Ye are bought with a price; be not ye the
servants of men (or anyone else I might add).
Blessed souls are bought with the blood of Christ,
1Pe 1:18-19 Forasmuch as ye know that ye were not redeemed with corruptible things, as silver and gold, from your vain conversation received by tradition from your fathers; But with the precious blood of Christ, as of a lamb without blemish and without spot:
Being a possession of God he can therefore graciously send a spirit into our lives,
Rom 8:9 Now if any man have not the Spirit of Christ, he is none of his.
Gal 4:6 because ye are sons, God hath sent forth the Spirit of his Son into your hearts…
Only Christians have this grace…and being so indwellt we worship and serve (not under compulsion) the Lord only.
Col 3:24…for ye serve the Lord Christ.
So again, IMO, one of the reasons demons possess is to get worship and service, due to God, out of those whom thoe whom they possess.