Whereas the Romish-Arminian cannot invest all his faith because he believes that some of his own perceived "meritous" faculties are necessary to cooperate unto salvation.

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Westminster Confession of Faith.
14/1. The grace of faith, whereby the elect are enabled to believe to the saving of their souls,a is the work of the Spirit of Christ in their hearts,b and is ordinarily wrought by the ministry of the Word;c by which also, and by the administration of the sacraments and prayer, it is increased and strengthened.d

a. Heb 10:39. • b. Eph 1:17-19; 2:8; 2 Cor 4:13. • c. Rom 10:14, 17. • d. Luke 17:5; Acts 20:32; Rom 1:16-17; 4:11; 1 Pet 2:2.

2. By this faith a Christian believeth to be true whatsoever is revealed in the Word, for the authority of God himself speaking therein;a and acteth differently upon that which each particular passage thereof containeth; yielding obedience to the commands,b trembling at the threatenings,c and embracing the promises of God for this life and that which is to come.d But the principal acts of saving faith are accepting, receiving, and resting upon Christ alone for justification, sanctification, and eternal life, by virtue of the covenant of grace.e

The unbiblical Arminian humanistic ideology comes from the natural man therefore is dominated by sin. The "religious" theory which is to be found in the natural man excludes the fact that he is Totally Depraved, he therefore considers himself to be less sinful than he really is.
Thus do we find the Arminian convinced that sin does not have influence over his mind and will and sin is perceived by them as less of a problem in their religious ideology.
This gives rise to their belief that they can contribute to their own salvation - viz salvation by works - DIY salvation - faith is human ability etc.
This ideology produces idolatry where their "Image" of god is that he is of a lesser power than the Sovereign God of the Bible.
A diminished god and an elevated sinner provides the basis for their religion. Whereby man can save himself by his own volition or faculty of faith. God and Christ become less necessary and Arminian religious theory is adapted to include a human philosophy of increased mortal autonomy.
God and Christ can thus be excluded or seen as only equal or incidental in the decisions about salvation.

Q34: How was the COVENANT OF GRACE administered under the Old Testament?

A34: The COVENANT OF GRACE was administered under the Old Testament, by promises,[1] prophecies, [2] sacrifices,[3] circumcision,[4] the passover,[5] and other types and ordinances, which did all foresignify Christ then to come, and were for that time sufficient to build up the elect in faith in the promised Messiah,[6] by whom they then had full remission of sin, and eternal salvation.[7]

1. Rom. 15:8
2. Acts 3:20, 24
3. Heb. 10:1
4. Rom. 4:11
5. I Cor. 5:7
6. Heb. ch. 8-10; 11:13
7. Gal. 3:7-9, 14

Q35: How is the COVENANT OF GRACE administered under the New Testament?

A35: Under the New Testament, when Christ the substance was exhibited, THE SAME COVENANT OF GRACE was and still is to be administered in the preaching of the word,[1] and the administration of the sacraments of Baptism [2] and the Lord’s Supper;[3] in which grace and salvation are held forth in more fulness, evidence, and efficacy, to all nations.[4]

John Yurich wrote:
What would be the problem with Bush becoming Catholic even if Bush is a Born Again Christian? If Bush became a Catholic all he would have to do would be to dispense with the unscriptural Catholic doctrines, adhere only to the scriptural Catholic doctrines,

God teaches

9 Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son.

AND
10 If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:
AND
11 For he that biddeth him God speed is partaker of his evil deeds.

So the true Christian must standfast for God and His Son Jesus - rejecting all cults and heresy.

That is Witness IN Truth.

Remember John; Bible commands