Numbers 19:9
“And a man that is clean shall gather up the ashes of the heifer, and lay them up without the camp in a clean place, and it shall be kept for the congregation of the children of Israel for a water of separation: it is a purification for sin.”

The purpose of the thinking man’s filter is separation. It is separation from sin, which is unbelief. To sin is to deny the Word and disbelieve, and the attributes of that sin is all the things we associate with it, such as lust, adultery, drinking, and those things. When the Scripture says in Ⅰ John 3:9, “Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.” It means that we are born again in Christ, new creatures, unable to deny the Word because Christ now lives in us. To deny the Word would be to deny ourselves.
When Christ does this work of restoration, we live in heavenly places in Christ Jesus, born anew. This is shown in Numbers chapter 19, when God describes how a person must be purified from sin by the water of separation. The thinking man then becomes separated from unbelief and purified by sin, when they take on the Spiritual mind. The world no longer has a hold on the thinking man, his filter only takes in what pleases God.
God calls for total separation from unbelief. A Believer will separate himself from anything that denies the Word and that is the reason the filter for a holy person becomes the Word of God. The Message of the Hour establishes that this is the Grace of God bringing us out of Babylon, separated from unbelief, into our promised land, the Holy Spirit.
A thinking man’s filter comes for separation and purification of sin.
65-0822E - “A Thinking Man's Filter”
And then when Israel sinned, and recognized that they had done wrong, then they were sprinkled with the ashes of this heifer, upon them. And that was the water of separation, a purification for sin. Notice. Here it is! And when Israel, before they could come into fellowship in the worship, they had to first pass through the waters of separation. "Justification by faith; cometh by hearing, hearing the Word." Then they entered into the congregation under those seven stripes, the blood, to show that something died and went before them, for their sin. They were separated by hearing the Word, the waters of separation, then entered into fellowship. The only place that God met a man was behind that order. He wouldn't meet him anywhere else. He had to come behind that order. God only met Israel in one place. And God only meets you today in one place, and that's in Jesus Christ; and He is the Word, the waters of separation. And His Blood was shed for all Seven Church Ages. And then, by the Holy Spirit, we enter into that fellowship, which is only given to the Church. Oh, how great He is!
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Acts 9-10