This is taken from the Kelly commentary
Sorry for the cut and paste.
But there is another thing. In watching against hasty and harsh judgment, there might be the abuse of grace. And the Lord immediately couples this with the former: "Give not that which is holy unto the dogs, neither cast ye your pearls before swine, lest they trample them under their feet, and turn again and rend you." We must carefully remember that the Lord is not here speaking about the gospel going out to sinners. God forbid that we should not carry out the grace of God to every quarter under heaven, because nothing less than this ought to be the desire and effort of every saint of God. All ought to have the spirit of active love going out after others, energetic desires for the salvation and the blessing of souls; for it were a sad shortcoming if it went not beyond souls being brought to Christ. Seeking to grow up into Christ and glorify Him in all things, to know and do the will of God is our calling. In this verse the Lord is not taking up the question of the gospel going out indiscriminately; for, if there be a difference, the gospel best suits those called "dogs", which, to the Jews, was a figure of all that is abominable. Speaking of thieves, drunkards, extortioners, etc., the apostle says: "Such were some of you; but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God."
It might be asked, Is not the wickedness of one man greater than that of another? On an earthly platform, one might say, Much every way; but God does not, in saving souls, make these distinctions. So, speaking of believers from among the Jews, the apostle says they had been "children of wrath, even as others." There may have been highly moral characters among them. Did this dispose them better towards God's grace? Alas, where the soul finds a justification of itself in what it is, nothing can be more dangerous. The apostle himself had been an example of this very thing. It is a hard thing for a man who had been building on his righteousness to bow to the truth that he can only enter heaven upon the ground of a publican and a sinner. But so it must be, if the soul is to receive salvation from God through the faith of Jesus.
The Lord, then, is not in anywise restraining the gospel from going out to every quarter; but He speaks of the relations of His own people with the unholy. The believer is not to bring out for these the special treasures that are the Christian portion. The gospel is the riches of God's grace to the world. But, besides the gospel, we have the special affections of Christ to the Church, His loving care for His servants, the hope! of His coining again, the glorious prospects of the Church as His bride, etc. If you were to talk about these things, which we may call the pearls of the saints, with those out of Christ, you are on wrong ground. If you were to insist upon the duties of the faithful in worldly company, then it is giving that which is holy unto the dogs. There is blessed provision for "the dogs" - the crumbs that fall from the Master's table. And such is the great grace of God toward us, that the crumbs which fall to our portion, Gentiles as we were, are the best.
Whatever may be the benefits promised to the Jew, the grace of God has brought out in the gospel fuller blessings than ever was promised to Israel. What can Israel have to compare with the mighty deliverance of God that we know now? The consciousness of being completely cleansed from all sin; of having the righteousness of God for ours at once and for ever in Christ; of present access to Him as Father through a rent veil; and made His temple through the Holy Ghost dwelling in us. As the Lord Himself said to the woman of Samaria, If thou knewest the gift of God, and who it is that saith to thee, Give Me to drink, thou wouldst have asked of Him, and He would have given thee living water." Where Christ is received now, by whomsoever it may be, there is this fulness of blessing, and the well is within the believer. "The water that I shall give hilt shall be in him a well of water, springing up into everlasting life." Thus we may see how wide and perfect is His grace, while it forbids certain things being thrown indiscriminately among the ungodly. Any act that implies fellowship between a believer and an unbeliever is false. Take, for instance, the question of worship, and the habit of calling the whole round of devotions worship. Worship supposes communion with the Father and the Son, and with each other in it. But the system which, founded on an easy rite which pretends to regenerate all, unites believers and unbelievers in one common form and calls it worship, is casting what is holy unto dogs. Is it not a thinly-disguised attempt to put the sheep and dogs upon the same ground? In vain. You cannot unite before God the enemies of Christ and those that belong to Him. You cannot mingle as one people those that have got life and those that have not. The attempt to do so is sin, and constant dishonour of the Lord. All effort to have a worship of this mixed character is going in the very teeth of the sixth verse.
On the other hand, preaching the gospel, where it is kept distinct from worship, is right and blessed. When the day of judgment comes upon this world, where does the worst stroke fall? Not upon the openly profane world, but upon Babylon, because Babylon is the confusion of what is of Christ with evil - the attempt to make communion between light and darkness. "Come out of her, My people," says the Lord, "that ye be not partakers of her sins, and that ye receive not of her plagues." Partaker of her sins is the grave affair with God. It is the acceptance of a common ground upon which the Church and the world can join; when the very object of God, and that for which Christ died, was that He might have a separate people unto Himself, so as to be, by their very consecration unto God, a light in this world - not a witness of pride, saying, "Stand by, I am holier than thou," but Christ's epistle, that tells the world where the living water is to be found, and bids them come: "Whosoever will, let him take of the water of life freely."
Where we do not confound the religion of the world with the worship that goes up to God from His people, there you will also have the true line of demarcation - where we ought to judge and where we ought not. There will be active service towards the world with the gospel, but a careful separation of the Church from the world. This is also true individually. Yet persons take advantage of the word of God that says, "If an unbeliever bid you to a feast, and ye be disposed to go," etc.; but take care how you go, and for what. If you go self-confident, you will but dishonour Christ; if to please yourself, this is poor ground; if to please other people, it is little better.
There may be occasions when the love of Christ would constrain a soul to go and bear a testimony to His love in a worldly company, yet if we knew how easily words may be said, and things done, that imply communion with that which is contrary to Christ, there would be fear and trembling; but where there is self-confidence, there never can be the power of God.