Our heavenly Father is the Faithful One. Jesus Christ is "the faithful Witness" (Rv 1:5), "The Faithful and True" (Rv 19:11). The Holy Spirit is the Spirit of truth, that is, of faithfulness (see Jn 16:13). The triune God is perfectly faithful (see 1 Thes 5:24). Even "if we are unfaithful He will still remain faithful, for He cannot deny Himself." It is God's nature to be faithful.
God calls us to be holy, to be like Him. That means that we must be faithful. Have you been faithful to your baptismal promises? This is the fundamental responsibility to which we must be faithful. Have you been faithful to your vocations as married, lay single, religious, parent, child, worker in the world, or church worker? Have you been faithful to the Church, including to your bishops, Pope, pastors, and brothers and sisters in Christ? Have you been faithful in keeping your word and your promises to those people the Lord has given you to love?
If you have been faithful, give God the glory, for it is only by His grace that you have been faithful. If you have not been faithful, repent, go to Confession, receive God's mercy, and become faithful. On Judgment Day, the Lord wants to say to each of us: "Well done! Good and faithful servant" (Mt 25:21, 23, our transl).