"In righteousness shalt thou be established: thou shalt be far from oppression; for thou shalt not fear: and from terror; for it shall not come near thee." (Isaiah 54: 14)
When we look over this passage, we need to recognize that we do not establish ourselves.
It has nothing to do with how we feel or what we do or think, but rather everything to do with what Jesus has done and what God our Father has done because of His Son:
"But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption:" (1 Corinthians 1: 30)
Christ is made to us righteousness. We do not make Him our righteousness. God gave Him to us:
"15But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many. 16And not as it was by one that sinned, so is the gift: for the judgment was by one to condemnation, but the free gift is of many offences unto justification. 17For if by one man's offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ." (Romans 5: 15-17)
"For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him." (2 Corinthians 5: 21)
Now, when we talk about being established in Christ, we are talking about God seating us in Christ.
First, of course, God the Father seated His Son at His right hand:
"19And what is the exceeding greatness of his power to us-ward who believe, according to the working of his mighty power, 20Which he wrought in Christ, when he raised him from the dead, and set him at his own right hand in the heavenly places, 21Far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come:" (Ephesians 1:19-21)
Now, when we understand where Jesus is seated, and how He got there, then we can understand where we are seated and how:
"4But God, who is rich in mercy, for his great love wherewith he loved us, 5Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;) 6And hath raised us up together, and made us sit together in heavenly places in Christ Jesus:" (Ephesians 2: 4-6)
When we receive this revelation, then we can understand all the promises, and why are they are Yea and Amen in Christ:
"20For all the promises of God in him are yea, and in him Amen, unto the glory of God by us. 21Now he which stablisheth us with you in Christ, and hath anointed us, is God; 22Who hath also sealed us, and given the earnest of the Spirit in our hearts." (2 Corinthians 1: 20-22)
In this verse, clearly God is establishing us. We do not establish ourselves, nor do we have to keep establishing ourselves:
"Wherefore he is able also to save them to the uttermost that come unto God by him, seeing he ever liveth to make intercession for them." (Hebrews 7: 25)