Here is how to know if you have become a Legalist.
its very simple to know.
Do you believe you can lose your salvation.
If you believe this, then you are becoming a legalist or you have become a legalist.
Legalism, the best way to understand it, is ........."i no longer trust that Christ keeps me saved".
See, a legalist can't honestly say ...>I believe that Christ keeps me saved".
They do not believe this.....They believe in commandments, and self effort, and the Torah, and the Law, and enduring to the end, and all the SELF EFFORT that has REPLACED faith in Christ to Keep them saved.
This is a matter of two theological systems of thought: Calvinism vs Arminianism. Holding to a more Arminian position does not make one a legalist in my view. Generally speaking, Arminians just don't believe in the same doctrines that Calvinists do.
Calvinism includes the belief that God’s grace is irresistible, while Arminianism says that an individual can resist the grace of God. Irresistible grace argues that when God calls a person to salvation, that person will inevitably come to salvation. Resistible grace states that God calls all to salvation, but that many people resist and reject this call.
Calvinism holds to perseverance of the saints while Arminianism holds to conditional salvation. Perseverance of the saints refers to the concept that a person who is elected by God will persevere in faith and will not permanently deny Christ or turn away from Him. Conditional salvation is the view that a believer in Christ can, of his/her own free will, turn away from Christ and thereby lose salvation. Note - many Arminians deny "conditional salvation" and instead hold to "eternal security."
There are those who believe in "once saved always saved" or the false Calvinist doctrine of "perseverance of the saints." If one knows that salvation can be lost they simply don't hold to the Calvinist doctrines of "total depravity" of "irresistible grace." In my view it does not make them legalistic. They just think that a person walking in the Spirit of God can out of his/her own free will choose willful sin and ultimately be overcome by this sin and lose salvation.
We are depraved, not totally depraved as the Calvinists teach. Calvinists teach that there is nothing a Christian can do to eternally separate themselves from God.
Here is a good resource for examining the arguments that oppose Calvinism:
https://www.simplybible.com/f172-tulip-p-perseverance-of-the-saints.htm
I will highlight two examples below of Calvinist and Arminian arguments that illustrate how these theological systems disagree over the Calvinist doctrine of "once saved always saved" or "perseverance of the saints."
1. Those who hold to the Calvinist doctrine of once saved always saved point out that the saved are "sealed by the Holy Spirit" (Ephesians 1:13). They that nobody could break the seal of Almighty God.
The seal is "the guarantee of our inheritance" (Ephesians 1:14). Three things are assured...
Firstly, the God of the elect knows them as his own (2Timothy 2:19).
Secondly, no enemy of the elect can snatch them from Christ's hand (John 10:28).
Thirdly, the elect themselves can remain faithful to God (Revelation 2:10).
This third guarantee is the scriptural version of the perseverance of the saints. The Arminians say it is one thing to guarantee people that they can be faithful till the end, and nobody can force them to lose their salvation. It is quite another thing to say they
cannot fall regardless of what they do.
2. Another argument for once saved always saved out that salvation is the free gift of God (Ephesians 2:8). It is reasoned that God would not be so fickle as to give a gift, and then later demand that it be returned to him.
The Arminians would say that God never changes his mind and retracts his promise, nor does God ever demand his gift back. By grace, he has given us the promise and hope of eternal life on the condition that we continue in the faith (Colossians 1:23).
Eternal life is a free gift in the sense that it is unmerited, not in the sense that it is unconditional. If I gave you a holiday as a free gift, it would be conditional upon you actually making the journey to the retreat. If you decided not to go, or got half way and decided to quit, that would not mean I had changed my mind or demanded my gift back. It would be all your doing.
Ultimately, it's a matter of what doctrines you believe in. This debate has been going on for a long time and each follower of the Lord should look at the doctrines to come to their own conclusions.
Here is a good resource for refuting the false doctrines of Calvin:
https://www.simplybible.com/f172-tulip-p-perseverance-of-the-saints.htm
Another good site for refuting the false doctrine of total depravity can be found here:
http://lhim.org/blog/2014/02/06/three-arguments-against-total-depravity/