Cast in thy lot among us; let us all have one purse:
Unity is nothing without God's approval! In fact, it is damnable treason, unless God approves! Sinners want saints to agree with them and join their projects, but the LORD God demands His children avoid and reject their close company (Pr 1:10,15). Sinners make great appeals for cooperation and friendship, but their hearts pursue very different goals.
Solomon here warned his son, and all young men, against the peer pressure of sinful men (Pr 1:10-19). See the comments on 1:10. Their goals were robbery and murder, and they would certainly be destroyed. Young men who fear the Lord should stay far from them and reject all appeals for joining together. Running with the gang is contrary to godliness!
Though it might seem safe to be united with the majority in some foolish or sinful endeavor, Solomon by God warned his son that no combined strength could protect from God's judgment (Pr 11:21). It is the wide gate and broad way, with many travelers joined happily together in the majority, that leads to destruction and death (Matt 7:13-14).
There is no safety or sanctuary from judgment in associating with sinners. An approving God that delights in your rejection of sin and sinners is the real sanctuary (Is 8:9-15). When nations gathered together against God's church in the Old Testament, He mocked their efforts, knowing He would empower His people to destroy them (Mic 4:11-13).
Fellowship and society with godly saints is wonderful (Ps 133:1; Phil 1:3-5), but it is horrible when saints are unequally joined together with unbelievers (Ps 144:11; I Cor 5:9-11)! Communion and unity in Christ's churches are great blessings (I Cor 12:12-27), but fellowship with sinners is damnable (Eph 5:11-12). Yet some good men with weak character cannot resist the invitations and pressure of wicked men to join with them.
Jehoshaphat was such a man. A grandson of David and king of Judah, he could not resist the invitations of Ahab, king of Israel, at joint projects and family intermarriage (II Chron 18:1-3). What saith the Lord? "And Jehu the son of Hanani the seer went out to meet him, and said to king Jehoshaphat, Shouldest thou help the ungodly, and love them that hate the LORD? therefore is wrath upon thee from before the LORD" (II Chron 19:2).
King Ahab had 400 prophets in full agreement in his ministerial association, but these were no match for one man who feared the LORD and would not join them. For one of the most interesting and powerful events in the Bible, read about the true prophet Micaiah rejecting their pleas for unity to declare God's word (I Kgs 22:1-40). Jehoshaphat was judged for joining with Ahab, but Micaiah was blessed for defying Ahab's 400 prophets.
The Tower of Babel was man's first known effort at uniting all the peoples of the earth, but the LORD stopped the work in its tracks and confounded all the participants! Glory! At the same site two thousand years later, King Nebuchadnezzar took his stab at religious ecumenism and unity, but three faithful men would not compromise truth at any cost and turned the religious festivities upside down! Glory!
God's children can only have true peace when purity is exalted - purity of truth and righteousness. "Come out from among them," is the holy cry of apostles and angels (II Cor 6:14-17; Rev 18:4). God's highest blessings and fellowship demand it (II Cor 6:16 - 7:1). There is no real peace where purity is sacrificed, only the peace of death (Pr 21:16). Churches must reject any holding contrary doctrine (Rom 16:17-18; Titus 3:10-11).
Godly men easily separate from those who do not fear God nor keep His commandments. Like Phinehas, they do not need to pray about the matter, they zealously take a javelin and end the party (Num 25:1-15). David did not want any compromisers near him (Ps 101:3-8), for he hated fools and sinners (Ps 26:5; 31:6; 139:21-22). Furthermore, he taught God's blessing on those who will separate from evildoers (Ps 1:1-3).
Moses left Egypt's pleasures and riches for the afflictions and reproach of Christ and His church (Heb 11:24-27). Could you make such a choice? Would you make it? There is comfort and reward, praise of men and human security, by staying in Pharaoh's house. But the great reward - the riches of Christ and an eternal inheritance in Him - are found only in Canaan, with a separated life. Are you willing to go alone with Jesus Christ, if you must go to Him outside the camp even of professing Christians (Heb 13:12-14)?