There are only three instances where casting of lots is mentioned in the New Testament: (1) When Zacharias’ turn came, by lot, to minister in the temple (Luke 1:9), (2) When the soldiers cast lots to divide the garments of Jesus (Matt 27:35), and (3) When Matthias was chosen by lot to take the place of Judas Iscariot as one among the Twelve (Acts 1:26). Following that, there is no mention of casting lots anymore in the Bible.
Scholars believe that this is so because we live in the Age of the Holy Spirit and every decision after Pentecost comes from Him.
In the Old Testament, however, God did command His people to decide a number of things on the basis of lots. For instance, the Scapegoat on the Day of Atonement had to be chosen by lot (Lev.16:8) and the Promised Land had to be divided among the tribes by lot (Num.26:55). In the book of Jonah we find that lots were cast to determine who the culprit was, and the lot rightly fell on Jonah. Lots were cast in serious matters where human capacities were exhausted and the only resolve was an appeal to the Higher Authority. It could never be done lightheartedly or with unbelief. The ones who cast the lots to make some decision couldn’t choose to doubt. Faith was integral to the whole procedure. They couldn’t, for instance, cast the lot and then say “Oh, let’s do it again. May be this just couldn’t be right. Anyway, it’s all a game of chance.” No, chance was a meaningless term here. Nothing happened by chance for someone who had faith. God was the one who held every element in the universe together. Therefore, it was declared: “The lot is cast into the lap, but its every decision is from the LORD.” (Prov.16:33).
The Old Testament was a world of shadows. Everything, including the material blessings and the various laws, pointed towards a higher reality: the sacrifices pointed to Christ, the Promised Land points to the True Rest, the material blessings point to the eternal inheritance of the saints. In the New Testament, faith and indecision can’t go together. If there is indecisiveness, we must ask God for wisdom (regarding what must be done) and the Holy Spirit is there to guide us (James 1:5). There is no need to cast lots anymore when it comes to matters of knowing God’s will. One must ask with faith without wavering and God will answer. In the same manner that one couldn’t doubt the decision of the lot in the Old Testament, one cannot doubt the guidance of the Holy Spirit and His control over our affairs when we surrender ourselves to Him in obedience to His Word. But, someone who wavers and keeps doubting and thinking “Oh, this might not be the right thing” and seeks other ways like trying to know what others think about this or that will never receive any wisdom from God. He will remain uncertain and doubt the whole thing, even if he did make a decision.
Of course, a carnal or an unspiritual person cannot understand the language of the Spirit.