What does it mean to be "in the Spirit"?

I keep coming upon the phrase **"in the Spirit"** in the NT. One search result of that phrase is here: https://www.blueletterbible.org/search/search.cfm?Criteria=%22in+the+spirit%22&t=NKJV#s=s_primary_0_1 A few examples are (NKJV): - Acts 19:21, **"Paul purposed in the Spirit"** - Romans 2:29, **"circumcision is that of the heart, in the Spirit, not in the letter"** - Romans 8:9, **"But you are not in the flesh but in the Spirit"** - Galatians 5:16, **"I say then: Walk in the Spirit, and you shall not fulfill the lust of the flesh"** It's possible that the phrase has different shades of meaning depending on the verse context. How are we to understand this phrase in a believer's life? I am asking for an answer from the Christian community that conforms to the Nicene Creed of 381 AD. A Pentecostal/charismatic viewpoint is welcome. Also, the tenor of some of these verses indicate that one is in the Spirit or in the flesh, so answers which adhere to this duality are preferred (answers that reflect grace under law to Christ rather than adherence to OT laws for righteousness).