The Holy Spirit would come upon people temporarily in the OT days to enable them to do a specific task--like in Sampson's case. When his hair was cut, the Holy Spirit left him; He didn't stay with them as He does now. We are indwelt, and He is always with us. Unfortunately, we don't allow Him to work in us as believers did in the past. Otherwise, we would do some great things as they did in the OT days and even as they did in Jesus' day.
No there was a difference. According to John 7:39 the Spirit had not yet been given also we see it in 14:16,17. So it is clear that there is a difference between the OT and NT saints in regards to the Spirit.
I am glad you agree that as Christians we are to keep the commandments and are also able since that is what scripture teaches. However the OT saints had the same ability according to scripture and Paul says while he was under the law he was blameless.
Though I might also have confidence in the flesh. If any other man thinketh that he hath whereof he might trust in the flesh, I more:
Circumcised the eighth day, of the stock of Israel, [of] the tribe of Benjamin, an Hebrew of the Hebrews; as touching the law, a Pharisee;
Concerning zeal, persecuting the church; touching the righteousness which is in the law, blameless.
A rightousness that was NOT same as that demanded by God though, unable to save anyone, as God demands perfection in the Law, a perfection of mind and heart, ONLY Jesus evr has and can keep it way God demanded!
Noah found favor in sight of the Lord, Joseph also
NONE were as jesus, HOLY and blameless in ALL of the Law!