By this will we have been sanctified through the offering of the body of Jesus Christ once for all.
Sanctification is what God did to separate us unto Him. Our spirit man within was sanctified (separated) from sin because we were given a new spirit. The old sinful spirit is gone. Consecration is our response to sanctification. Because of God’s work of sanctification (giving us a new spirit man within) we now consecrate ourselves (dealing with outward actions), dedicating ourselves unto God to have fellowship with Him in the beauty of holiness.
Without consecration you cannot have intimate fellowship with God. God loves everyone the same, but He does not fellowship with everyone the same as 1 Peter 1:15-16 tells us, that as God who called us is holy, we too should be holy in all our conduct. Consecration is what holiness is all about, for to be holy means you now set yourself apart from the worlds way of living unto God.
If we do not consecrate ourselves from sin we will harden our heart toward God. God is a Spirit and He bears witness with our spirit. If we don’t consecrate ourselves from sin we sear our conscience (the voice of our spirit man), and that will hinder our ability to hear from God and to therefore be led by Him. So live a consecrated life in gratitude of the sanctified work of Christ, and you can develop an intimate walk with God.