Why can't you serve two masters?
Scripture teaches God draws a line of demarcation between the believer and the world, just as He divided Israel from Egypt. Because God has set that division, a person cannot serve two masters; they will serve one and hate the other, or vice versa. Divided allegiance is impossible.
Les explains that just as God drew an invisible line around Goshen so even the insects would not cross, and put a division between Israel and Egypt, He also puts a line of demarcation between the believer and the world. Paul gives the same set of directions in 2 Corinthians 6. Since God has separated His people, He says you cannot serve two masters; you will serve one and hate the other, or vice versa. This echoes Romans 15:4, where the Old Testament lessons are written for our learning.