Partnership necessitates common purpose and agreement, and therefore to make an alliance we must have accepted the behaviour of our partner, unless we have acted in ignorance. On the assumption that we are not ignorant, then in order to make common cause with a thief we must have chosen to stifle any criticism of his thieving.
The warning is against any form of covenant the believer may make with this fallen world that weakens his ability to walk in the paths of righteousness. All friendships need to be examined carefully, and the believer’s standard need to be made crystal clear from the start so that any who wish to walk with us are well aware that we will not turn aside. The world is always trying to influence us, to intimidate us, and we must let the world know that if they wish to walk with us then it is they who must change by repentance and faith and adopt God’s standards, for we will not adopt their standards. The Christian is called to be incorruptible in a corrupt world.