God has always required faithfulness from His people. While on earth, Jesus commanded it of Thomas (John 20:27) and taught that all who would follow Him must manifest faithfulness (Luke 16:10-13). How can we know, though, if we are truly faithful to the Lord?
There is a measurement by which faithfulness can be determined. In Matthew 25, Jesus taught that the two approved servants in the parable of the talents were "good and faithful" while the other servant was "wicked and slothful" (v. 26). The word "slothful" is used as the opposite of "faithful." Vine's Expository Dictionary of NT Words says of "slothful" that it means "indolent, sluggish, synonym of 'dull,' also 'shirking and irking.'" The faithful servant, therefore, receives the master's blessing and approval because he has done the master's bidding. On the other hand, the slothful servant is condemned because he has failed to do that which his master required of him.
Jesus is plainly teaching that His servants will be called to give an accounting of what they have done and will be judged by their faithfulness (cf. 2 Cor. 5:10), i.e., whether or not they were obedient to the will of God.
Consider the charge to those who comprised the church in Smyrna. The Lord, through John, told them that if they were going to be recipients of the "crown of life," they would have to be "faithful" even to the point of death (Rev. 2:10).
The word "loyal" very aptly defines the word "faithful." Anyone who is faithful is loyal. A loyal American is one who is faithful to the principles upon which this country is founded. He is willing to defend his country in every way consistent with his conscience, to pay his taxes and to vote for the one he believes will work for the best interests of America.
In a much higher sense, a citizen of the kingdom of heaven (Phil. 3:20 - "For our citizenship is in heaven..."), if he is loyal, must be willing to defend the gospel (Jude 3); contribute of his means to advance the cause of Christ (2 Cor. 9:6-7); work untiringly in the work of the Lord (Titus 2:14); and share in the responsibilities of the church (Eph. 2:10).
Consider the example of the unfaithful husband. When a married man has been "unfaithful" to his wife, he has not been "loyal" to the vow he made to be faithful until they part in death.
The members of the church are the bride of Christ (Eph. 5:23-25). As such, they are to be faithful unto the bridegroom. When church members start missing services, fail to pray as they ought, fail to work as they should and forsake the church and take up with the world, they are unfaithful. When they go back into the world they, because of their unfaithfulness, are condemned to be lost unless they return to their first love.
There is another idea in the word "faithful." It is the idea of being steadfast.
The faithful Christian is one who is not tossed to and fro by every wind of doctrine (Eph. 4:14-15). He remains constant in his service to the Lord. He heeds such passages as Galatians 6:9 ("And let us not grow weary while doing good, for in due season we shall reap if we do not lose heart.") and 1 Corinthians 15:58 ("Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your labor is not in vain in the Lord.").
Faithfulness is a daily challenge which brings one into newness of life every day and ultimately provides the greatest reward imaginable. Let us all be determined to be faithful to Christ.