Matthew 5:17 says, “Don’t think that I came to abolish the law of the prophets; I didn’t come to abolish, but to fulfill.” The fundamental principle behind God’s law is His life. In the law, He was, in a limited way, putting into writing what His nature was like. The absence of idolatry and giving God the first place, honoring father and mother, never hurting other people with murder, adultery or any such thing, etc., was a manifestation of the life of God in man, and Jesus manifested that life. He said, “I haven’t come to abolish the law.” The fundamental principle behind the law was never abolished. Some people misunderstand that verse to mean that we should keep the Sabbath as well.

Colossians 2:16 says, “Don’t let anyone act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day, because all these things are a shadow.” Did you notice that He included the fourth commandment, keeping the Sabbath? He says it is only a shadow. It is fulfilled in Christ. In today’s language, you could say it is like a photograph. Until Christ came, you needed the photograph. If I am not travelling with my wife, I may carry her photograph with me and look at it, but if I am travelling with my wife, why do I need to look at the photograph? There is something wrong with a man who is travelling with his wife but keeps looking at her photograph!

The law is over, now that Christ has come. He says that was only a shadow. It is an accurate picture of Christ - many things in the Old Testament accurately portrayed Christ - but it is only a photograph. The reality is in Christ. We need to keep that in mind when Jesus speaks about fulfilling the law. The Sabbath was fulfilled in Christ, and now it’s the inner Sabbath that the Lord is seeking to bring into our hearts. “Come to Me and I will give you rest” (Matthew 11:28). That inner rest comes as we take His yoke upon us. Some people think of keeping the Sabbath as the one commandment that should never be cancelled. No, the fulfillment of the law is now through the Holy Spirit inside our hearts.

In Romans 8:4, it is explained like this: “The righteous requirement of the law is now fulfilled inside us, who do not walk according to the flesh, but according to the Spirit.” This is how the law is fulfilled. We have to compare Scripture with Scripture. The law will not pass away. Jesus did not come to abolish the law, but to fulfill it, and it must be fulfilled in us, too. How is it going to be fulfilled in us? The righteous requirement of the law is fulfilled in us when we don’t walk according to the flesh, but according to the Holy Spirit instead, every single day (Romans 8:4).It’s not by keeping the Sabbath or other commandments. 

Matthew 5:20, Jesus describes how completely we are to fulfill the law: “Unless your righteousness exceeds the righteousness of the scribes and Pharisees, you cannot enter the kingdom of heaven.” Jesus Christ came to fulfill the law, and even in our lives, the law of God has to be fulfilled in our hearts. In the Old Testament, they fulfilled it externally in various ways - they kept the “outside of the cup” clean. But it is the inside of the cup that God is interested in now. We are to be the salt of the earth and the light of the world, and that life has to come from the Holy Spirit, from within.

Philippians 2:12, 13 says, "Work out your salvation with fear and trembling, since it is God who is at work within you to will and to do of His good pleasure ".

Here are a couple of points concerning this verse:

(i) Salvation (in the past tense) is first of all salvation from the wrath and judgment of God. This salvation is a free gift from God and we can never work to get it. Jesus has "finished" it for us on the cross. But salvation also refers to being saved (present tense) from Adam's nature (the flesh) and our sinful, worldly behaviour (tone of voice, irritation, impurity, materialism, etc.). This is the salvation spoken of in the above verse. Here are the three tenses of our salvation:

We have been saved from the penalty of sin.

We are being saved from the power of sin.

We will be saved from the presence of sin one day, when Christ returns.

(ii) Whenever God's Word speaks about God working in us, it always refers to the ministry of the Holy Spirit. And His primary task is to sanctify us (set us apart from sin and the world) and to make us holy. So what God "works in " us, we have to "work out". When God speaks to us pointing out some attitude or thought or behaviour in us that needs to change, that is God "working in us". When we accept that correction and " cleanse ourselves from that particular filthiness of flesh or spirit that He points out " (see 2 Cor.7:1) - that particular habit in our life - then we are "working out our salvation".